Compositions and methods for production of myrcene

ABSTRACT

Provided herein are compositions and methods for producing myrcene by culturing genetically modified microbial host cells that express a myrcene synthase and optionally a geranyl pyroplosphate synthase. Also provided herein are isolated nucleic acid molecules that encode myrcene synthase variants derived from the Ocimum species myrcene synthase, which comprise one or more amino acid substitutions that improve in vivo performance of myrcene synthase in genetically modified microbial host cells. Also provided herein are isolated myrcene synthase variants that exhibit an improved activity for converting geranyl diphosphate into myrcene.

1. CROSS REFERENCE TO RELATED APPLICATION

This application is a Divisional of co-pending U.S. patent applicationSer. No. 15/771,888, filed on Apr. 27, 2018, which is the National Stageof PCT International Application No. PCT/US2016/059584, filed on Oct.28, 2016, which claims priority to U.S. Provisional Application No.62/248,240, filed on Oct. 29, 2015. The entirety of each of theseapplications is hereby incorporated by reference.

2. INCORPORATION BY REFERENCE

The present application contains a Sequence Listing which has beensubmitted in ASCII format via EFS-Web and is hereby incorporated byreference in its entirety. Said ASCII copy having been modified on Oct.25, 2016, is named “107345_00612_ST25.txt” and is 83,853 bytes in size.

3. FIELD OF THE INVENTION

The present invention relates to fermentation compositions, geneticallymodified microbial host cells, and isolated nucleic acid molecules forproducing myrcene from the genetically modified microbial host cells.

4. BACKGROUND

Among terpenes, monoterpenes, the C10 members of the terpenoid family,are the main constituents of essential oils that are naturally found inleaves, flowers and fruits. These essential oils have various functionsbetween plants and between plants and predators. For example, some ofmonoterpenes are involved in wound healing in plants. Examples ofmonoterpenes found in plants include limonene, myrcene, 3-carene,ocimene, pinene, and the like.

Monoterpenes are commercially important feedstocks for many industries.In particular, myrcene, is an important intermediate used in theperfumery industry. Myrcene can be derivatized to produce various endproducts including fragrances and flavors. While myrcene is found innature, it exists in small quantities. Furthermore, while somemonoterpenes, such as camphor, exist in a near pure form, myrcenegenerally exists as complex mixtures with other monoterpenes. Therefore,myrcene is difficult to isolate in large quantities from the complexmixtures.

Therefore, there is a need for an efficient and economical method forproducing myrcene in high quantities.

5. SUMMARY

Provided herein are compositions and methods comprising geneticallymodified microbial host cells comprising a heterologous nucleic acidmolecule encoding a myrcene synthase. It was discovered by the presentinventors that a myrcene synthase derived from Ocimum species, whenexpressed in genetically modified microbial host cells, produces myrcenein relatively high quantities. Variants of the wild-type Ocimum speciesmyrcene synthase are also generated using targeted mutagenesistechniques and screening of combinatorial libraries that contain variousmutations. The myrcene synthase variants provided herein exhibitimproved in vivo performance in terms of myrcene production and/orenzyme activity in genetically modified microbial host cells compared totheir parent myrcene synthase. Therefore, fermentation compositions andmethods provided herein can be used to produce myrcene in high quantityin an economic and reliable manner.

The monoterpene product profile produced by genetically modifiedmicrobial host cells comprising presently provided myrcene synthases isunique and distinguishable from those produced by other known myrcenesynthases. Therefore, the fermentation compositions can be used toproduce end products having unique properties, such as fragrance andflavor, which may be distinguishable from monoterpenes produced by othermyrcene synthases.

In one aspect, provided herein is a fermentation composition comprising:(a) a genetically modified microbial host cell cultured in a culturemedium, wherein the genetically modified microbial host cell comprises aheterologous nucleic acid molecule encoding a myrcene synthase; and (b)monoterpenes produced from the genetically modified microbial host cell,wherein the monoterpenes comprise myrcene as a major component and oneor more co-products as minor components, wherein the one or moreco-products comprise α-terpinene and/or γ-terpinene. In certainembodiments, one or more monoterpene co-products in the fermentationcomposition further comprise 4-terpineol. In certain embodiments, one ormore monoterpene co-products in the fermentation composition furthercomprise sabinene, limonene, β-ocimene, and β-linalool. In certainembodiments, one or more monoterpene co-products in the fermentationcomposition further comprise α-thujene, (E)-sabinene hydrate, and/or(Z)-sabinene hydrate.

In certain embodiments, the monoterpenes in the fermentation compositioncomprise at least about 85% myrcene and less than about 15% one or moreco-products, compared to a total amount of the monoterpenes, based onrelative area % of the monoterpenes in a GC-MS chromatogram. In certainembodiments, the monoterpenes in the fermentation composition comprisebetween about 88% to about 93% myrcene, compared to the total amount ofthe monoterpenes, based on relative area % of the monoterpenes in theGC-MS chromatogram. In certain embodiments, the monoterpenes comprise,based on the total amount of the monoterpenes: about 89.09% to about92.01% myrcene, about 0.80% to about 0.98% sabinene, about 0.67% toabout 0.90% α-terpinene, about 0.54% to about 1.01% limonene, about0.91% to about 1.21% β-ocimene, about 1.00% to about 1.06% γ-terpinene,about 0.76% to about 1.17% β-linalool, and about 2.32% to about 2.42%4-terpineol, based on relative area % of the monoterpenes in the GC-MSchromatogram. In certain embodiments, the monoterpenes further comprise,based on the total amount of the monoterpenes: about 0% to about 0.51%α-thujene, about 0% to about 0.54% (E)-sabinene hydrate, and about 0.98%to about 1.13% (Z)-sabinene hydrate, based on relative area % of themonoterpenes in the GC-MS chromatogram. In certain embodiments, thefermentation composition comprises at least 50 mg, at least 100 mg, atleast 500 mg, at least 1 gram, at least 5 grams, at least 10 grams, atleast 50 grams, at least 100 grams, or at least 150 grams of myrcene perliter of the culture medium.

In another aspect, the fermentation composition comprises microbial hostcells that are genetically modified to comprise a heterologous nucleicacid molecule encoding a myrcene synthase of an Ocimum species or avariant thereof. In some embodiments, the myrcene synthase comprises anamino acid sequence that has at least about 70%, at least about 75%, atleast about 80%, at least about 85%, at least about 90%, at least about95%, at least about 96%, at least about 97%, at least about 98%, atleast about 99% sequence identity to the myrcene synthase of Ocimumspecies. In certain embodiments, the myrcene synthase comprises an aminoacid sequence having at least about 70%, at least about 75%, at leastabout 80%, at least about 85%, at least about 90%, at least about 95%,at least about 96%, at least about 97%, at least about 98%, or at leastabout 99% sequence identity to SEQ ID NO: 2. In certain embodiments, themyrcene synthase comprises an amino acid sequence having at least about70%, at least about 75%, at least about 80%, at least about 85%, atleast about 90%, at least about 95%, at least about 96%, at least about97%, at least about 98%, or at least about 99% sequence identity to SEQID NO: 2, and comprises at least one variant amino acid residue comparedto SEQ ID NO: 2 at one or more of positions selected from the groupconsisting of 27, 28, 207, 213, 222, 342, 347, 381, 382, 389, 390, 401,404, 428, 439, 466, 482, 484, 505, 514, 517, 524, 527, 528, 543, 544,and 552, wherein the positions are numbered with reference to SEQ ID NO:2. In certain embodiments, the myrcene synthase comprises an amino acidsequence having at least about 70%, at least about 75%, at least about80%, at least about 85%, at least about 90%, at least about 95%, atleast about 96%, at least about 97%, at least about 98%, or at leastabout 99% sequence identity to SEQ ID NO: 2, and comprises at least onevariant amino acid residue selected from the group consisting of H27I,H27C, S28H, I207V, K213C, K213H, K213R, K213V, R222N, C342L, Y347R,F381L, V382L, D389G, D389S, G390D, N401I, N401V, I404V, V428L, Y439L,A466C, A466S, R482C, R482D, R482H, R482I, R482L, R482N, R482V, H484Y,C505I, C505L, C505V, G514L, G514V, S517G, F524L, F524V, V527C, V527F,V527H, V527L, V527N, V527S, V527Y, E528D, M543I, A544S, and Q552R,wherein the positions are numbered with reference to SEQ ID NO: 2. Incertain embodiments, the myrcene synthase comprises an amino acidsequence of SEQ ID NO: 2, except that the amino acid sequence comprisesone or more variant amino acid residues relative to SEQ ID NO:2, asdescribed herein.

In certain embodiments, the genetically modified microbial host cells inthe fermentation composition comprise a heterologous nucleic acidmolecule encoding a myrcene synthase that comprises at least one set ofvariant amino acid residues compared to SEQ ID NO: 2, and wherein the atleast one set of variant amino acid residues is selected from the groupof sets of variant amino acid residues consisting of: (a) F381L, I404V,E528D, and M543I; (b) I404V and E528D; (c) F381L, D389G, I404V, Y439L,and E528D; (d) F381L, E528D, and M543I; (e) F381L, I404V, and E528D; (f)F381L, I404V, E528D, and A544S; and (g) F381L, I404V, E528D, and Q552R,wherein the positions are numbered with reference to SEQ ID NO: 2. Incertain embodiments, the heterologous nucleic acid molecule encoding themyrcene synthase comprises a nucleotide sequence having at least about70%, at least about 75%, at least about 80%, at least about 85%, atleast about 90%, at least about 95%, at least about 96%, at least about97%, at least about 98%, or at least about 99% sequence identity to SEQID NO: 1, SEQ ID NO: 3, or SEQ ID NO: 4. In certain embodiments, theheterologous nucleic acid molecule encodes a myrcene synthase whichcomprises one or more amino acid variants described above.

In another aspect, the fermentation composition comprises geneticallymodified microbial host cells that further comprise a heterologousnucleic acid molecule encoding a geranyl pyrophosphate synthase. Thegeranyl pyrophosphate synthase catalyzes the formation of geranylpyrophosphate, which is a substrate for a myrcene synthase. In certainembodiments, the geranyl pyrophosphate synthase is derived from abacterium. In certain embodiments, the geranyl pyrophosphate synthase isderived from a Streptomyces species, in particular Streptomycesaculeolatus. In certain embodiments, the heterologous nucleic acidmolecule encoding a geranyl pyrophosphate synthase comprises an aminoacid sequence that has at least about 70%, at least about 75%, at leastabout 80%, at least about 85%, at least about 90%, at least about 95%,at least about 96%, at least about 97%, at least about 98%, at leastabout 99%, or 100% sequence identity to SEQ ID NO: 7. In certainembodiments, the heterologous nucleic acid molecule encoding the myrcenesynthase and the heterologous nucleic acid molecule encoding the geranylpyrophosphate synthase are chromosomally integrated into the genome ofthe genetically modified microbial host cells.

In certain embodiments, the genetically modified microbial host cells inthe fermentation composition further comprise at least one heterologousmevalonate pathway gene encoding an enzyme selected from the groupconsisting of: (a) an enzyme that condenses two molecules ofacetyl-coenzyme A to form acetoacetyl-CoA; (b) an enzyme that condensesacetoacetyl-CoA with another molecule of acetyl-CoA to form3-hydroxy-3-methylglutaryl-CoA (HMG-CoA); (c) an enzyme that convertsHMG-CoA into mevalonate; (d) an enzyme that converts mevalonate intomevalonate 5-phosphate; (e) an enzyme that converts mevalonate5-phosphate into mevalonate 5-pyrophosphate; (f) an enzyme that convertsmevalonate 5-pyrophosphate into IPP; and (g) an enzyme that converts IPPinto DMAPP. In certain embodiments, the genetically modified microbialhost cell comprises an endogenous farnesyl pyrophosphate which isfunctionally disrupted to direct carbon flow towards production ofgeranyl pyrophosphate.

In another aspect, genetically modified microbial host cells areprovided. In certain embodiments, a genetically modified microbial hostcell comprises: (a) a heterologous nucleic acid molecule encoding anOcimum species myrcene synthase that comprises: (i) the amino acidsequence of SEQ ID NO: 2; or (ii) an amino acid sequence that has atleast 70%, at least about 75%, at least about 80%, at least about 85%,at least about 90%, at least about 95%, at least about 96%, at leastabout 97%, at least about 98%, at least about 99% sequence identity toSEQ ID NO: 2; and (b) a heterologous nucleic acid molecule encoding ageranyl pyrophosphate synthase. In certain embodiments, the heterologousnucleic acid molecule encoding a geranyl pyrophosphate synthase isderived from a bacterium. In certain embodiments, the geranylpyrophosphate synthase is derived from a Streptomyces aculeolatusgeranyl pyrophosphate synthase. In certain embodiments, the heterologousnucleic acid molecule encodes a geranyl pyrophosphate synthase thatcomprises: (i) the amino acid sequence of SEQ ID NO: 7; or (ii) an aminoacid sequence that has at least about 70%, at least about 75%, at leastabout 80%, at least about 85%, at least about 90%, at least about 95%,at least about 96%, at least about 97%, at least about 98%, at leastabout 99% sequence identity to SEQ ID NO: 7. In certain embodiments, themyrcene synthase in the microbial host cell comprises at least onevariant amino acid residue compared to SEQ ID NO: 2 at one or morepositions selected from the group consisting of 27, 28, 207, 213, 222,342, 347, 381, 382, 389, 390, 401, 404, 428, 439, 466, 482, 484, 505,514, 517, 524, 527, 528, 543, 544, and 552, wherein the positions arenumbered with reference to SEQ ID NO: 2. In certain embodiments, themyrcene synthase in the microbial host cell may comprise one or morevariant amino acid residues described above.

In another aspect, isolated nucleic acid molecules encoding myrcenesynthase variants are provided. In certain embodiments, the isolatednucleic acid molecule encodes a myrcene synthase comprising: (a) anamino acid sequence that has at least about 70%, at least about 75%, atleast about 80%, at least about 85%, at least about 90%, at least about95%, at least about 96%, at least about 97%, at least about 98%, or atleast about 99% sequence identity to SEQ ID NO: 2; and (b) at least onevariant amino acid residue compared to SEQ ID NO: 2 at one or morepositions 27, 28, 207, 213, 222, 342, 347, 381, 382, 389, 390, 401, 404,428, 439, 466, 482, 484, 505, 514, 517, 524, 527, 528, 543, 544, and552, wherein the positions are numbered with reference to SEQ ID NO: 2.In certain embodiments, at least one variant amino acid residue encodedby the isolated nucleic acid molecules is selected from the groupconsisting of H27I, H27C, S28H, I207V, K213C, K213H, K213R, K213V,R222N, C342L, Y347R, F381L, V382L, D389G, D389S, G390D, N401I, N401V,I404V, V428L, Y439L, A466C, A466S, R482C, R482D, R482H, R482I, R482L,R482N, R482V, H484Y, C505I, C505L, C505V, G514L, G514V, S517G, F524L,F524V, V527C, V527F, V527H, V527L, V527N, V527S, V527Y, E528D, M543I,A544S, and Q552R, wherein the positions are numbered with reference toSEQ ID NO: 2.

In certain embodiments, the isolated nucleic acid molecule encodes amyrcene synthase comprising at least one set of variant amino acidresidues compared to SEQ ID NO: 2, and wherein the at least one set ofvariant amino acid residues is selected from the group of sets ofvariant amino acid residues consisting of: (a) F381L, I404V, E528D, andM543I; (b) I404V and E528D; (c) F381L, D389G, I404V, Y439L, and E528D;(d) F381L, E528D, and M543I; (e) F381L, I404V, and E528D; (f) F381L,I404V, E528D, and A544S; and (g) F381L, I404V, E528D, and Q552R, whereinthe positions are numbered with reference to SEQ ID NO: 2.

In certain embodiments, the isolated nucleic acid molecule comprises anucleotide sequence having at least about 70%, at least about 75%, atleast about 80%, at least about 85%, at least about 90%, at least about95%, at least about 96%, at least about 97%, at least about 98%, or atleast about 99% sequence identity to SEQ ID NO: 1, SEQ ID NO: 3, or SEQID NO: 4. In certain embodiments, one or more codons in the isolatednucleic acid molecule encodes at least one variant amino acid residueselected from the group consisting of H27I, H27C, S28H, I207V, K213C,K213H, K213R, K213V, R222N, C342L, Y347R, F381L, V382L, D389G, D389S,G390D, N401I, N401V, I404V, V428L, Y439L, A466C, A466S, R482C, R482D,R482H, R482I, R482L, R482N, R482V, H484Y, C505I, C505L, C505V, G514L,G514V, S517G, F524L, F524V, V527C, V527F, V527H, V527L, V527N, V527S,V527Y, E528D, M543I, A544S, and Q552R, wherein the positions arenumbered with reference to SEQ ID NO: 2.

In another aspect, an isolated mutant myrcene synthase is provided. Incertain embodiments, the isolated mutant myrcene synthase has at leastabout 70%, at least about 75%, at least about 80%, at least about 85%,at least about 90%, at least about 95%, at least about 96%, at leastabout 97%, at least about 98%, at least about 99% amino acid sequenceidentity to SEQ ID NO: 2 and exhibits an improved activity forconverting geranyl diphosphate into myrcene compared to the activity ofa myrcene synthase of SEQ ID NO: 2 under identical reaction conditions.In certain embodiments, the mutant myrcene synthase comprises a variantamino acid residue located at one or more of positions 27, 28, 207, 213,222, 342, 347, 381, 382, 389, 390, 401, 404, 428, 439, 466, 482, 484,505, 514, 517, 524, 527, 528, 543, 544, or 552, wherein the positionsare numbered with reference to SEQ ID NO: 2. In certain embodiments, themutant myrcene synthase comprises at least one variant amino acidresidue selected from the group consisting of H27I, H27C, S28H, I207V,K213C, K213H, K213R, K213V, R222N, C342L, Y347R, F381L, V382L, D389G,D389S, G390D, N401I, N401V, I404V, V428L, Y439L, A466C, A466S, R482C,R482D, R482H, R482I, R482L, R482N, R482V, H484Y, C505I, C505L, C505V,G514L, G514V, S517G, F524L, F524V, V527C, V527F, V527H, V527L, V527N,V527S, V527Y, E528D, M543I, A544S, and Q552R, wherein the positions arenumbered with reference to SEQ ID NO: 2.

In another aspect, vectors comprising the isolated nucleic acidmolecules described herein are provided.

In another aspect, a method of producing myrcene is provided. The methodcomprises culturing a genetically modified microbial host cell describedherein in a culture medium under culture conditions suitable forproduction of myrcene. In certain embodiments, the method of producingmyrcene comprises: (a) culturing a population of a genetically modifiedmicrobial host cell in a first culture medium under a non-inducingcondition, wherein the genetically modified microbial host cellcomprises a heterologous nucleic acid molecule encoding a myrcenesynthase and a heterologous nucleic acid molecule encoding a geranylpyrophosphate synthase; and (b) culturing the population or asubpopulation thereof in a second culture medium under an inducingcondition which increases production of myrcene compared to thenon-inducing condition of step (a), wherein the second culture mediumcomprises monoterpenes produced from the population or subpopulation ofthe genetically modified microbial host cell. In certain embodiments,the monoterpenes comprise myrcene as a major component and one or moreco-products as minor components. In certain embodiments, one or moreco-products comprise α-terpinene and γ-terpinene. In certainembodiments, the method of producing myrcene further comprisesrecovering myrcene from the culture medium. In certain embodiments, thegenetically modified microbial host cells are cultured in a culturemedium with an overlay. In certain embodiments, the genetically modifiedmicrobial host cells are cultured in a sealed container.

6. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates an overview of myrcene production in a microbial hostcell. In the schematic diagram shown in FIG. 1 , the microbial host cellconverts feedstocks (e.g., sugar or other carbohydrates) to producemyrcene via the mevalonate pathway. To produce myrcene, geranylpyrophosphate synthase (GPPS) and myrcene synthase (MyrS) can beincorporated into a microbial host cell to divert carbon flux from theC5-prenyl diphosphate metabolites isopentenyl diphosphate (IPP) anddimethyallyl diphosphate (DMAPP) to geranyl diphosphate (GPP). In someembodiments, FPP synthase (FPPS, e.g., encoded by ERG20 in S.cerevisiae) may be modulated, for example, functionally disrupted, toachieve maximum production of myrcene.

FIG. 2A is a schematic depiction of the mevalonate pathway.

FIG. 2B is a schematic depiction of the 1-deoxy-D-xylulose 5-diphosphate(DXP) pathway.

FIG. 3A illustrates chromatograms from GC-FID: Top trace, myrcene andco-products produced from genetically modified microbial host cellsexpressing Ocimum basilicum myrcene synthase (ObMS); bottom trace,myrcene and co-products produced from genetically modified microbialhost cells expressing Quercus ilex (QiMS). The monoterpene productionprofiles of various myrcene synthases were tested using both GC-MS andGC-FID. GC-MS was used in particular to identify co-products includingocimene, phenethyl alcohol, linalool, and geraniol. Phenylethyl alcoholand geraniol were excluded from the myrcene area % purity calculationsince phenylethyl alcohol is not a terpene and geraniol is likely notproduced by the action of myrcene synthase but rather by yeast-derivedpyrophosphatases. Only monoterpenes, which are identified by presence ofmolecular ion 136 (C10 terpene) on the GC-MS chromatograms as wellmolecular ion 154 (C10 terpene alcohol) are considered in the puritycalculation. GC-FID detector was subsequently used to obtain moreaccurate area % monoterpene production profile data.

FIG. 3B illustrates GC-MS chromatogram zoomed in C10 terpenoid range ofcompounds produced by yeast host cells comprising Ocimum basilicummyrcene synthase. Assigned compound structures are listed in FIG. 4 .

FIG. 3C illustrates linearity of myrcene signal response (area) as afunction of sample concentration. For material purity assessment, thehighest sample concentration, where biggest peak still remains withinlinear range of detector response, is used for data accuracy. Based onthis data, 3 μl of sample at 0.5 g/L was chosen as appropriate foranalysis in Example 7.7.

FIG. 4 illustrates chemical structures of compounds identified inmonoterpenes produced by yeast host cells heterologously expressingOcimum basilicum myrcene synthase.

FIG. 5 provides a comparison of myrcene production in a straincomprising the Streptomyces aculeolatus geranyl pyrophosphate synthase(SaGPPS) gene and a strain comprising Abies grandis (AgGPPS) gene, bothof which are codon optimized for expression in S. cerevisiae. Each GPPSwas integrated as a single copy and ObMS was expressed on a high copyplasmid 2μ/Leu2d. Each flask was sampled at 72 hours, and the myrcenetiters were determined by GC chromatograph. Error bars show standarddeviation for 3 replicates.

FIG. 6 illustrates comparison of the in vivo performance of the improvedObMS variants when integrated as a single copy in strain X100. The1×ObMS is encoded by a wild-type myrcene synthase nucleic acid of Ocimumbasilicum comprising SEQ ID NO: 1. The 1×ObMS was selected as the baseenzyme (parent) to engineer. The 5×ObMS nucleic acid was created fromcodon optimization of the 1×ObMS nucleic acid for optimal expression inSaccharomyces cerevisiae. The 5×ObMS nucleic acid comprises a nucleotidesequence of SEQ ID NO: 3. The 14×ObMS nucleic acid was derived fromdirected evolution using 5×ObMS as parent. The 14×ObMS nucleic acidcomprises a nucleotide sequence of SEQ ID NO: 4. The Y-axis is themyrcene production level at 72 hours as measured using limonene as aninternal standard.

FIG. 7 illustrates two confirmed ObMS variants with improved myrceneproduction over their parent, 14×ObMS, based on the competition assay.The ObMS variant with mutation at residue 552 has an amino acidsubstitution from glutamine to arginine. The ObMS variant with amutation at residue 544 has an amino acid substitution from alanine toserine. The Y-axis provides the percent improvement over the parentenzyme. Replicates of five (for parent) and twelve (for the twovariants) were used in this experiment.

7. DETAILED DESCRIPTION OF THE EMBODIMENTS

Provided herein are compositions and methods for the efficientbiosynthesis of myrcene, particularly via genetic engineering of myrcenesynthases. In one embodiment, the production of myrcene is provided inhigh quantities in microorganisms that normally do not produce myrcene.In another embodiment, provided herein are compositions and methods forproducing myrcene by culturing genetically modified microbial host cellsthat express a myrcene synthase derived from an Ocimum species. Incertain embodiments, provided herein are isolated nucleic acid moleculesthat encode myrcene synthase variants derived from the wild-type Ocimumbasilicum myrcene synthase, wherein the variants comprise one or moreamino acid substitutions that improve in vivo performance of the enzymein genetically modified microbial host cells. In certain embodiments,provided herein are isolated myrcene synthase variants that exhibit animproved activity for converting geranyl diphosphate into myrcenecompared to wild-type myrcene synthases.

7.1 Definitions

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Reference is made here to anumber of terms that shall be defined to have the following meanings:

The term “monoterpenes” are a class of terpenes that consist of twoisoprene units. As used herein, the term “monoterpene” is also intendedto include “monoterpenoid,” which refers to a compound in which the C10skeleton of the parent monoterpene has been modified, for example, byoxidation, or rearrangement of the carbon skeleton, and may be linear orcyclic.

The term “co-product” refers to a monoterpene that is co-produced withmyrcene by genetically modified microbial host cells comprising amyrcene synthase through the catalytic reaction of the myrcene synthase.As used herein, myrcene and its co-products make up the total amount ofmonoterpenes produced from genetically modified microbial host cells.

As used herein, the term “the total amount of monoterpenes” producedfrom genetically modified microbial host cells exclude geraniol in thecalculation of the total amount of monoterpenes or in the calculation ofpurity of myrcene produced by the microbial host cells. This is becausegeraniol is likely generated from myrcene synthase-independenthydrolysis of geranyl pyrophosphate in genetically modified microbialhost cells.

As used herein, % refers to % measured as relative area % by GC-MS orGC-FID, unless specifically indicated otherwise. A relative area %refers to a ratio between an area of a peak of interest divided by a sumof all of the areas of peaks in the chromatogram multiplied by 100%.Thus, as used herein, % monoterpene in a mixture of monoterpenes isbased on peak area normalization of a gas chromatography-massspectrometer (GC-MS) or gas chromatography-flame ionization detector(GC-FID) chromatogram. As described above, a peak associated withgeraniol is excluded from the sum of all of the areas of peaksassociated with monoterpenes. In certain embodiments, % of eachmonoterpene produced from genetically modified microbial host cells ismeasured under GC-MS conditions described in Example 7.7, and therelative area percent is calculated using 3 μl of sample at 0.5 g/Lconcentration of myrcene.

As used herein, the term “GC chromatogram” refers to an electronicand/or graphic record of data representing the absolute or relativequantitative detection of a plurality of separated chemical speciesobtained or derived from a group of molecules, where separation has beenperformed by a GC-MS or a GC-FID.

As used herein, the term “major component” in a mixture of compoundsrefers to a compound which comprises at least about 50%, at least about55%, at least about 60%, at least about 65%, at least about 70%, atleast about 75%, at least about 80%, at least about 85%, at least about90%, or at least about 95%, compared to the total amount of compounds.With reference to monoterpenes produced from genetically modifiedmicrobial host cells, myrcene is a major component compared to the totalamount of monoterpenes produced from the microbial host cells, based onrelative area % of monoterpene peaks in a GC chromatogram as describedin Example 7.7.

As used herein, the term “minor component(s)” in a mixture of compoundsrefer to one or more compounds which comprise, individually orcollectively, less than about 50%, less than about 45%, less than about40%, less than about 35%, less than about 30%, less than about 25%, lessthan about 20%, less than about 15%, less than about 10%, less thanabout 5%, less than about 4%, less than about 3%, less than about 2%, orless than about 1%, compared to the total amount of compounds. Withreference to monoterpenes produced from genetically modified microbialhost cells, co-products are minor components compared to the totalamount of monoterpenes produced from the genetically modified microbialhost cells, based on relative area % of monoterpene peaks in a GCchromatogram as described in Example 7.7.

As used herein, the term “substantially free” of a compound in a mixtureof compounds refers to a compound having less than 0.1% of the compoundbased on the total amount of compounds based on relative area % ofcompound peaks in a GC chromatogram.

In the following description, all numbers disclosed herein areapproximate values, regardless of whether the word “about” or“approximate” is used in connection therewith. Numbers may vary by 1%,2%, 5%, or by 10 to 20%. Whenever a numerical range with a lower limitR^(L) and an upper limit R^(U) is disclosed, any number falling withinthe range is specifically disclosed. In particular, the followingnumbers R_(k) within the range are specifically disclosed:R_(k)=R^(L)+k*(R^(U)−R^(L)), wherein k is a variable ranging from 0.01to 1 with a 0.01 increment, i.e., k is 0.01, 0.02, 0.03, 0.04, 0.05, . .. , 0.5, 0.51, 0.52, . . . , 0.95, 0.96, 0.97, 0.98, 0.99, or 1.Further, any numerical range defined by any two numbers R_(k) as definedabove is also specifically disclosed herein.

The term “myrcene” or “β-myrcene,” also known as7-methyl-3-methylene-1,6-octadiene, is a monoterpene having themolecular formula C₁₀H₁₆ and has the following molecular structure:

The term “sabinene,” also known as4-methylene-1-(1-methylethyl)bicyclo[3.1.0]hexaner, is a monoterpenehaving the molecular formula C₁₀H₁₆ and has the following structure or astereoisomer thereof:

The term “α-terpinene,” also known as1-Isopropyl-4-methyl-1,3-cyclohexadiene, is a monoterpene having themolecular formula of C₁₀H₁₆ and has the following structure:

The term “limonene,” also known as1-methyl-4-(1-methylethenyl)-cyclohexene, is a monoterpene having themolecular formula of C₁₀H₁₆ and has the following structure or astereoisomer thereof:

The term “β-ocimene,” also known as cis-3,7-dimethyl-1,3,7-octatriene,is a monoterpene having the molecular formula of C₁₀H₁₆ and has thefollowing structure or a stereoisomer thereof:

The term “γ-terpinene,” also known as4-methyl-1-(1-methylethyl)-1,4-cyclohexadiene, is a monoterpene havingthe molecular formula of C₁₀H₁₆ and has the following structure:

The term “β-linalool,” also known as 3,7-dimethylocta-1,6-dien-3-ol, isa monoterpene product having the molecular formula of C₁₀H₁₈O and hasthe following structure or a stereoisomer thereof:

The term “α-thujene,” also known as1-isopropyl-4-methylbicyclo[3.1.0]hex-3-ene, is a monoterpene having themolecular formula of C₁₀H₁₆ and has the following structure or astereoisomer thereof:

The term “(E)-sabinene hydrate,” also known as(1S,4R,5R)-4-methyl-1-propan-2-ylbicyclo[3.1.0]hexan-4-ol, is amonoterpene having the molecular formula of C₁₀H₁₈O and has thefollowing structure or a stereoisomer thereof:

The term “(z)-sabinene hydrate,” also known as4-methyl-1-propan-2-ylbicyclo[3.1.0]hexan-4-ol, is a monoterpene havingthe molecular formula of C₁₀H₁₈O and has the following structure or astereoisomer thereof:

As used herein, to “functionally disrupt” or a “functional disruption”e.g., of a target gene, for example, a gene encoding FPP synthase, meansthat the target gene is altered in such a way as to decrease in the hostcell the activity of the protein encoded by the target gene. Similarly,to “functionally disrupt” or a “functional disruption” e.g., of a targetprotein, for example, FPP synthase, means that the target protein isaltered in such a way as to decrease in the host cell the activity ofthe protein. In some embodiments, the activity of the target proteinencoded by the target gene is eliminated in the host cell. In otherembodiments, the activity of the target protein encoded by the targetgene is decreased in the host cell. Functional disruption of the targetgene may be achieved by deleting or mutating all or a part of the geneso that gene expression is eliminated or reduced, or so that theactivity of the gene product is eliminated or reduced. Functionaldisruption of the target gene may also be achieved by deleting ormutating a regulatory element of the gene, e.g., the promoter of thegene so that expression is eliminated or reduced, or by deleting ormutating the coding sequence of the gene so that the activity of thegene product is eliminated or reduced. In some embodiments, functionaldisruption of the target gene results in the removal of the completeopen reading frame of the target gene.

The term “fermentation” is used to refer to culturing microorganismsthat utilize carbon sources, such as sugar, as an energy source toproduce a desired product.

The term “culture medium” refers to a medium which allows growth ofbiomass and production of microbial metabolites. It contains a source ofcarbon and may further contain a source of nitrogen, a source ofphosphorus, a source of vitamins, a source of minerals, and the like.

As used herein, the term “fermentation medium” may be used synonymouslywith “culture medium.” Generally, the term “fermentation medium” may beused to refer to a medium which is suitable for culturing microorganismsfor a prolonged time period to produce a desired compound frommicroorganisms.

The term “medium” refers to a culture medium and/or fermentation medium.The “medium” can be liquid or semi-solid. A given medium may be both aculture medium and a fermentation medium.

The term “whole cell broth” refers to the entire contents of a vessel(e.g., a flask, plate, fermentor and the like), including cells, aqueousphase, compounds produced in hydrocarbon phase and/or emulsion. Thus,the whole cell broth includes the mixture of a culture medium comprisingwater, carbon source (e.g., sugar), minerals, vitamins, other dissolvedor suspended materials, microorganisms, metabolites and compoundsproduced by microorganisms, and all other constituents of the materialheld in the vessel in which monoterpenes including myrcene is being madeby the microorganisms.

The term “fermentation composition” is used interchangeably with “wholecell broth.” The fermentation composition can also include an overlay ifit is added to the vessel during fermentation.

The term “biosynthetic pathway” refers to a pathway with a series ofenzymes leading to the biosynthesis of a molecule.

The term “mevalonate pathway” or “MEV pathway” is used herein to referto a biosynthetic pathway that can convert acetyl-CoA to IPP. Oneembodiment of the MEV pathway is shown in FIG. 2A. The mevalonatepathway comprises enzymes that catalyze the following steps: (a)condensing two molecules of acetyl-CoA to form acetoacetyl-CoA; (b)condensing acetoacetyl-CoA with acetyl-CoA to form3-hydroxy-3-methylglutaryl-CoA (HMG-CoA); (c) converting HMG-CoA tomevalonate; (d) phosphorylating mevalonate to mevalonate 5-phosphate;(e) converting mevalonate 5-phosphate to mevalonate 5-pyrophosphate; and(f) converting mevalonate 5-pyrophosphate to isopentenyl pyrophosphate(IPP). The “top half” of the mevalonate pathway refers to the enzymesresponsible for the conversion of acetyl-CoA to mevalonate through a MEVpathway intermediate. In certain embodiments, the IPP isomerase, whichconverts IPP into DMAPP, is also referred to as a MEV pathway enzyme.

The term “deoxyxylulose 5-phosphate pathway” or “DXP pathway” is usedherein to refer to the biosynthetic pathway that convertsglyceraldehyde-3-phosphate and pyruvate to IPP and DMAPP through aseries of enzymes, which are referred to as DXP pathway enzymes. Oneembodiment of the DXP pathway is illustrated schematically in FIG. 2B.

The term “pyrophosphate” is used interchangeably herein with“diphosphate.”

The term “myrcene synthase” refers to an enzyme capable of catalyzingthe formation of myrcene as a major product from a geranyl pyrophosphateprecursor (also referred to as geranyl diphosphate precursor). Thecatalytic reaction of myrcene synthase may concurrently produce otherco-products as minor components in addition to myrcene. For example, amyrcene synthase is capable of producing at least about 50%, at leastabout 60%, at least about 70%, at least about 80%, at least about 85%,at least about 90%, at least about 95%, at least about 96%, at leastabout 97%, at least about 98%, or at least about 99% myrcene, comparedto the total amount of monoterpenes produced by microbial host cellsgenetically modified with the myrcene synthase, based on relative area %of monoterpenes in a GC chromatogram. As used herein, the term “myrcenesynthase” may include a bifunctional enzyme which catalyzes twodifferent catalytic reactions using two different substrates.

The term “geranyl pyrophosphate synthase” refers to a polypeptidecapable of catalyzing the formation of geranyl pyrophosphate bycondensing precursors, isopentenyl pyrophosphate (IPP) and dimethylallylpyrophosphate (DMAPP) together. As used herein, the term “geranylpyrophosphate synthase” may include a bifunctional enzyme whichcatalyzes two different catalytic reactions using two differentsubstrates.

As used herein, the term “sequence identity” or “percent identity,” inthe context or two or more nucleic acid or protein sequences, refer totwo or more sequences or subsequences that are the same or have aspecified percentage of amino acid residues or nucleotides that are thesame. For example, the sequence can have a percent identity of at least70%, at least 75%, at least 80%, at least 85%, at least 90%, at least91% at least 92%, at least 93%, at least 94%, at least 95%, at least96%, at least 97%, at least 98%, at least 99%, or higher identity over aspecified region to a reference sequence when compared and aligned formaximum correspondence over a comparison window, or designated region asmeasured using a sequence comparison algorithm or by manual alignmentand visual inspection. For example, percent of identity is determined bycalculating the ratio of the number of identical nucleotides (or aminoacid residues) in the sequence divided by the length of the totalnucleotides (or amino acid residues) minus the lengths of any gaps.

For convenience, the extent of identity between two sequences can beascertained using computer program and mathematical algorithms known inthe art. Such algorithms that calculate percent sequence identitygenerally account for sequence gaps and mismatches over the comparisonregion. Programs that compare and align sequences, like Clustal W(Thompson et al., (1994) Nucleic Acids Res., 22: 4673-4680), ALIGN(Myers et al., (1988) CABIOS, 4: 11-17), FASTA (Pearson et al., (1988)PNAS, 85:2444-2448; Pearson (1990), Methods Enzymol., 183: 63-98) andgapped BLAST (Altschul et al., (1997) Nucleic Acids Res., 25: 3389-3402)are useful for this purpose. The BLAST or BLAST 2.0 (Altschul et al., J.Mol. Biol. 215:403-10, 1990) is available from several sources,including the National Center for Biological Information (NCBI) and onthe Internet, for use in connection with the sequence analysis programsBLASTP, BLASTN, BLASTX, TBLASTN, and TBLASTX. Additional information canbe found at the NCBI web site.

In certain embodiments, the sequence alignments and percent identitycalculations can be determined using the BLAST program using itsstandard, default parameters. For nucleotide sequence alignment andsequence identity calculations, the BLASTN program is used with itsdefault parameters (Gap opening penalty=5, Gap extension penalty=2,Nucleic match=1, Nucleic mismatch=−3, Expectation value=10.0, Wordsize=11). For polypeptide sequence alignment and sequence identitycalculations, BLASTP program is used with its default parameters (Gapopening=11, Gap extension penalty=2; Nucleic match=1; Nucleicmismatch=−3, Expectation value=10.0; Word size=11; matrix Blosum 62).Alternatively, the following program and parameters are used: Align Plussoftware of Clone Manager Suite, version 5 (Sci-Ed Software); DNAcomparison: Global comparison, Standard Linear Scoring matrix, Mismatchpenalty=2, Open gap penalty=4, Extend gap penalty=1. Amino acidcomparison: Global comparison, BLOSUM 62 Scoring matrix.

As used herein, the term “homology” refers to the identity between twoor more nucleic acid sequences, or two or more amino acid sequences.Sequence identity can be measured in terms of percentage identity (orsimilarity or homology); the higher the percentage, the more near toidentical the sequences are to each other. Homologs or orthologs ofnucleic acid or amino acid sequences possess a relatively high degree ofsequence identity when aligned using standard methods. For example, a“homolog” of a reference protein or nucleic acid includes a protein ornucleic acid which has at least about 50%, at least about 55%, at leastabout 60%, at least about 65%, at least about 70%, at least about 75%,at least about 80%, at least about 85%, at least about 90%, at leastabout 95%, at least about 96%, at least about 97%, at least about 98%,at least about 99% sequence identity to the reference protein or nucleicacid, respectively. As discussed above, various programs for sequencealignment and analysis are well known, and can be used to determinewhether two sequences are homologs of each other.

The phrase “stringent hybridization conditions” refers to conditionsunder which a probe will hybridize to its target subsequence, typicallyin a complex mixture of nucleic acids, but to no other sequences.Stringent conditions are sequence-dependent and will be different indifferent circumstances. Longer sequences hybridize specifically athigher temperatures. An extensive guide to the hybridization of nucleicacids is found in Tijssen, Techniques in Biochemistry and MolecularBiology—Hybridization with Nucleic Probes, “Overview of principles ofhybridization and the strategy of nucleic acid assays” (1993).Generally, stringent conditions are selected to be about 5-10° C. lowerthan the thermal melting point (T_(m)) for the specific sequence at adefined ionic strength pH. The T_(m) is the temperature (under definedionic strength, pH, and nucleic concentration) at which 50% of theprobes complementary to the target hybridize to the target sequence atequilibrium (as the target sequences are present in excess, at T_(m),50% of the probes are occupied at equilibrium). Stringent conditions mayalso be achieved with the addition of destabilizing agents such asformamide. For selective or specific hybridization, a positive signal isat least two times background, preferably 10 times backgroundhybridization. Exemplary stringent hybridization conditions can be asfollowing: 50% formamide, 5×SSC, and 1% SDS, incubating at 42° C., or,5×SSC, 1% SDS, incubating at 65° C., with wash in 0.2×SSC, and 0.1% SDSat 65° C.

Nucleic acids that do not hybridize to each other under stringentconditions are still substantially identical if the polypeptides whichthey encode are substantially identical. This occurs, for example, whena copy of a nucleic acid is created using the maximum codon degeneracypermitted by the genetic code. In such cases, the nucleic acidstypically hybridize under moderately stringent hybridization conditions.Exemplary “moderately stringent hybridization conditions” include ahybridization in a buffer of 40% formamide, 1 M NaCl, 1% SDS at 37° C.,and a wash in 1×SSC at 45° C. A positive hybridization is at least twicebackground. Those of ordinary skill will readily recognize thatalternative hybridization and wash conditions can be utilized to provideconditions of similar stringency. Additional guidelines for determininghybridization parameters are provided in numerous reference, e.g.,Current Protocols in Molecular Biology, ed. Ausubel et al.

A “conservative amino acid substitution” is one in which an amino acidresidue is substituted by another amino acid residue having a side chain(R group) with similar chemical properties (e.g., charge orhydrophobicity). In general, a conservative amino acid substitution willnot substantially change the functional properties of a protein. Incases where two or more amino acid sequences differ from each other byconservative substitutions, the percent sequence identity or degree ofhomology may be adjusted upwards to correct for the conservative natureof the substitution. Means for making this adjustment are well known tothose of skill in the art (See, e.g., Pearson W. R., 1994, Methods inMol. Biol 25: 365-89).

The following six groups each contain amino acids that are conservativesubstitutions for one another: 1) Serine (S), Threonine (T); 2) AsparticAcid (D), Glutamic Acid (E); 3) Asparagine (N), Glutamine (Q); 4)Arginine (R), Lysine (K); 5) Isoleucine (I), Leucine (L), Alanine (A),Valine (V); and 6) Phenylalanine (F), Tyrosine (Y), Tryptophan (W).

As used herein, the term “variant amino acid residue” refers to an aminoacid change or an amino acid substitution in a variant form of areference protein. For example, a variant amino acid residue “F381L”refers that position 381 of a reference protein, which normally hasphenylalanine (F), is substituted with amino acid residue leucine (L) inthe variant protein. In another example, a variant amino acid residue“D389G” refers that position 389 of a reference protein, which normallyhas amino acid residue aspartic acid (D), is substituted with amino acidresidue glycine (G) in the variant protein.

As used herein, the term “myrcene synthase variant” or “mutant myrcenesynthase” with reference to an amino acid sequence refers to a myrcenesynthase that has a different amino acid sequence compared to areference myrcene synthase (e.g., a wild-type myrcene synthase). Themyrcene synthase variant or mutant myrcene synthase may comprise aminoacid additions, deletions, substitutions and/or insertions, compared toits reference myrcene synthase. The term “myrcene synthase variant” or“mutant myrcene synthases” nucleic acid molecule with reference to anucleotide sequence refers to a myrcene synthase nucleic acid moleculethat has a different nucleotide sequence compared to a reference myrcenesynthase nucleic acid molecule. For example, compared to the wild-typemyrcene synthase nucleic acid molecule, a myrcene synthase variantnucleic acid molecule or a mutant myrcene synthase nucleic acid moleculemay comprise nucleotide addition(s), deletion(s), and/or substitution(s)that may or may not result in changes to the corresponding amino acidsequence. In some embodiments where nucleotide changes do not result inchanges to the amino acid sequence, the changes may nonetheless effectimproved activity of the myrcene synthase, for example, through codonoptimization.

As used herein, the term “reference” or “parent” sequence (e.g., nucleicacid or protein) refers to a sequence selected for sequence comparison,enzyme activity comparison, or myrcene production comparison with avariant sequence (e.g., nucleic acid or protein).

As used herein, the term “native” or “endogenous” refers to a substanceor process that can occur naturally in a host cell.

As used herein, the term “genetically modified” denotes a host cell thatcomprises a heterologous nucleotide sequence.

As used herein, the term “heterologous” refers to what is not normallyfound in nature. For example, the term “heterologous” when used withrespect to a nucleic acid (DNA or RNA) or protein refers to a nucleicacid or protein that does not occur naturally as part of the organism,cell, genome, or DNA or RNA sequence in which it is present, or that isfound in a cell or location or locations in the genome or DNA or RNAsequence that differ from that in which it is found in nature. The term“heterologous compound” refers to the production of a compound by a cellthat does not normally produce the compound, or to the production of acompound at a level at which it is not normally produced by the cell.

As used herein, the term “naturally occurring” refers to what is foundin nature. For example, a myrcene synthase that is present in anorganism that can be isolated from a source in nature and that has notbeen intentionally modified by a human in the laboratory is naturallyoccurring myrcene synthase. Conversely, as used herein, the term“naturally not occurring” refers to what is not found in nature but iscreated by human intervention.

As used herein, the term “in vivo performance” or “activity” of amyrcene synthase refers to its ability to convert a geranylpyrophosphate to myrcene when expressed in a microbial host cell.Accordingly, the term “improved in vivo performance” or “improvedactivity” refers to an increased ability of a myrcene synthase toconvert a geranyl pyrophosphate to myrcene when expressed in a microbialhost cell.

As used herein, the phrase “heterologous enzyme” refers to an enzymethat is not normally found in a given cell in nature. The termencompasses an enzyme that is: (a) exogenous to a given cell (i.e.,encoded by a nucleotide sequence that is not naturally present in thehost cell or not naturally present in a given context in the host cell);and (b) naturally found in the host cell (e.g., the enzyme is encoded bya nucleotide sequence that is endogenous to the cell) but that isproduced in an unnatural amount (e.g., greater or lesser than thatnaturally found) in the host cell.

The terms “amino acid sequence,” “peptide,” “oligopeptide,”“polypeptide” and “protein” are used here interchangeably, and refer toa polymeric form of amino acids of any length which may or may not bechemically or biochemically modified.

The terms “polynucleotide” and “nucleic acid” are used hereinterchangeably, referring to polymeric forms of any length, bothribonucleotides and deoxyribonucleotide.

The term “isolated nucleic acid” or “isolated nucleic acid molecule,”when applied to DNA, refers to a DNA molecule that is separated fromsequences with which it is immediately contiguous in the naturallyoccurring genome of the organism in which it originated. An “isolatednucleic acid” or “isolated nucleic acid molecule” also includesnon-genomic nucleic acids such as cDNA or other non-naturally occurringnucleic acid molecules.

The term “cDNA” is defined herein as a DNA molecule which can beprepared by reverse transcription from a mature, spliced, mRNA moleculeobtained from a cell. cDNA lacks intron sequences that are usuallypresent in the corresponding genomic DNA.

As used herein, the phrase “operably linked” refers to a functionallinkage between nucleic acid sequences such that the linked promoterand/or regulatory region functionally control expression of the codingsequence.

As used herein, the term “productivity” refers to production of acompound by a host cell, expressed as the amount of a compound produced(by weight) per amount of fermentation medium in which the host cell iscultured (by volume) over time (per hour). As applied to myrcene, theterm “productivity” refers to production of myrcene by a host cell,expressed as the amount of myrcene produced (by weight) per amount offermentation medium in which the host cell is cultured (by volume) overtime (per hour).

As used herein, the term “yield” refers to production of a compound by ahost cell, expressed as the amount of the compound produced per amountof carbon source consumed by the host cell, by weight. Morespecifically, as applied to production of myrcene, the term “yield”refers to the amount of myrcene generated compared with total reducingsugar added to a fermentor vessel or a flask (i.e., grams of myrceneproduced divided by grams of total reducing sugar added, expressed aspercentage). The total reducing sugar is a unit of measurement of sugarin grams. A reducing sugar is any sugar that is capable of acting as areducing agent because it has a free aldehyde group or a free ketonegroup. All monosaccharides, such as galactose, glucose, and fructose,are reducing sugars. For example, if 10 grams of myrcene is produced byfeeding host cells 100 grams of glucose (i.e., 100 grams of reducingsugar), then the yield of myrcene is 10%.

The term “titer” or “concentration” refers to production of a compoundby a host cell, expressed as the amount of a compound produced (byweight) per volume of fermentation medium in which the host cell iscultured.

The term “a,” “an,” and “the” means “at least one” unless the contextclearly indicates otherwise.

7.2 Biosynthetic Pathways for Production of Myrcene

Myrcene is an aromatic hydrocarbon which is an important part of theessential oils of a number of different plants. It is a monoterpene,which is derived from the C5 compound isopentyl pyrophosphate (IPP). Asshown in FIG. 1 , the biosynthetic steps leading from IPP tomonoterpenes include two enzymes, geranyl pyrophosphate synthase (GPPS)and myrcene synthase (MyrS). In order to produce myrcene, both GPPS andMyrS are typically required in genetically modified microbial hostcells, although certain terpene synthases are known to be bifunctionalas GPPS and MyrS. Generally, GPPS diverts the carbon flux from theC5-prenyl diphosphate metabolites isopentenyl diphosphate (IPP) anddimethylallyl diphosphate (DMAPP) to geranyl diphosphate (GPP). MyrS, inturn, can convert the GPP precursor to myrcene. While FIG. 1 illustratesmyrcene as the only monoterpene produced by the catalytic reaction of amyrcene synthase with a geranyl pyrophosphate, a number of othermonoterpenes may be concurrently produced as minor components by certainmyrcene synthases.

Furthermore, while FIG. 1 illustrates using the mevalonate pathway forproduction of myrcene, the present compositions and methods are notlimited to using the mevalonate pathway for the production of myrcene.Two different pathways leading to IPP and DMAPP exist: the mevalonatepathway (MEV pathway) and non-mevalonate pathway (DXP pathway).Eukaryotes, with the exception of plants, generally use the mevalonatedependent pathway. As shown in FIG. 2A, the MEV pathway uses acetyl CoAas the initial precursor to produce IPP and its isomer DMAPP through aseries of MEV pathway enzymes. Prokaryotes, with some exceptions,typically employ only the DXP pathway to produce IPP and DMAPP. Plantsuse both the MEV pathway and DXP pathway. As shown in FIG. 2B, the DXPpathway uses glyceraldehyde-3-phosphate and pyruvate as the initialprecursors to produce IPP and its isomer DMAPP through a series of DXPpathway enzymes. In certain embodiments, either the MEV pathway or DXPpathway enzymes may be utilized to produce precursors for biosynthesisof myrcene in genetically modified microbial host cells.

In compositions and methods provided herein, a microbial host cell isgenetically modified to comprise a heterologous myrcene synthasesequence. In certain embodiments, the microbial host cell is furthergenetically modified to comprise a heterologous geranyl pyrophosphatesynthase sequence. In some embodiments, additional heterologous nucleicacid molecules (e.g., MEV or DXP pathway genes) may be introducedtogether with the heterologous myrcene synthase and the heterologousgeranyl pyrophosphate synthase to enhance the production of myrcene ingenetically modified microbial host cells. In certain embodiments, oneor more endogenous genes of the host genome may be functionallydisrupted or modified to improve myrcene production in geneticallymodified microbial host cells.

7.3 Myrcene Synthases and its Variants

A number of myrcene synthase genes have been previously isolated andannotated as myrcene synthases in the literature. While some of themhave been characterized biochemically, none of them have been shown tobiosynthetically produce myrcene in high quantity in geneticallymodified microbial host cells. It has been discovered by the presentinventors that compared to myrcene synthase sequences obtained fromother organisms, the myrcene synthases derived from Ocimum species, inparticular Ocimum basilicum, are capable of providing relatively highproduction of myrcene in genetically modified microbial host cells.

Furthermore, as shown in the examples section, both wild-type Ocimumbasilicum and its variants, when expressed in genetically modifiedmicrobial host cells, exhibit a unique monoterpene product profile,which is distinguishable from monoterpene product profiles produced bymyrcene synthases derived from other organisms. For example, thepresently provided myrcene synthases, when expressed in geneticallymodified microbial host cells, produce α-terpinene and γ-terpinene asco-products together with myrcene. However, other myrcene synthases,such those derived from Quercus ilex do not produce α-terpinene andγ-terpinene as co-products with myrcene. See, e.g., FIG. 3A. Therefore,the product profile of the presently provided myrcene synthase sequenceshave a unique molecular fingerprint and is distinguishable from theproduct profile of other myrcene synthase sequences. As a result, theycan be utilized to produce end products, such as fragrances and flavors,with potentially distinct characteristics (e.g., odor or flavor profile)which may differ from those produced by other myrcene synthases.

Thus, provided herein are myrcene synthase sequences, which, whenexpressed in genetically modified microbial host cells, produce myrcenein relatively high quantity with a distinct monoterpene product profile.In certain embodiments, the wild-type myrcene synthase sequences fromOcimum species are codon optimized for a selected microbial host cell toproduce myrcene. In certain embodiments, the myrcene synthase variantsare provided where one or more amino acid positions of the wild-typemyrcene synthases are altered to further improve in vivo performance ofthe enzymes to enhance myrcene production, purity, and/or productprofile.

7.3.1. Myrcene Synthase Variant Amino Acid Sequences

Provided herein are myrcene synthase variants which includemodification(s) of amino acid residues compared to a reference sequenceand yet still retain the biological activity as a myrcene synthase. Inone embodiment, the reference myrcene synthase is a wild-type myrcenesynthase of Ocimum basilicum (ObMS) comprising amino acid sequence SEQID NO: 2. In another embodiment, the reference myrcene synthase may be ahomolog of the myrcene synthase of Ocimum basilicum. For example, thereference myrcene synthase may be myrcene synthases from Ocimum speciesother than Ocimum basilicum which share a substantial sequence identitywith SEQ ID NO: 2. In some embodiments, myrcene synthase variants mayalso be generated from other homologs or orthologs of the Ocimumbasilicum myrcene synthase from different organisms.

As used herein, the term “wild-type” myrcene synthase refers to atruncated form of naturally occurring myrcene synthases without theN-terminal transit peptide. Terpene synthases derived from plantsincluding the myrcene synthase preprotein of Ocimum basilicum include anN-terminal transit peptide sequence (also referred to asplastid-targeting sequence) which is necessary in plants to import thenuclear-encoded plastid protein into plastids. In microbial host cells,the N-terminal transit peptide sequence is not necessary for expression.As such, to express Ocimum basilicum or other myrcene synthases inmicrobial host cells, the N-terminal transit peptide in the myrcenesynthase preprotein is truncated to remove the N-terminal transitpeptide sequence. An exemplary embodiment of Ocimum basilicum myrcenesynthase nucleotide sequence without the transit peptide sequence isshown as SEQ ID NO: 1 (also referred to as 1×ObMS nucleic acid), and thecorresponding amino acid sequence is shown as SEQ ID NO: 2.

Myrcene synthase variants according to certain embodiments may includeamino acid substitutions, deletions, additions, and/or insertions atcertain amino acid positions compared to a reference myrcene synthase.The deletions or additions may occur at the N-terminus or C-terminus ofthe reference protein. In one embodiment, an amino acid sequence may beadded to one or both terminal ends of the reference protein. Forexample, an amino acid sequence may be added to the reference myrcenesynthase to increase the myrcene synthase stability in myrcene synthasevariants. In another embodiment, myrcene synthase variants may include adeletion of a non-functional portion of the enzyme. For example, amyrcene synthase variant may include a deletion of one, two, three, orfour amino acid residues at the N-terminus compared to a referencesequence of SEQ ID NO: 2. The amino acid sequence of SEQ ID NO: 2, whichis a truncated wild-type Ocimum basilicum myrcene synthase, includesRR(×)8W motif sequences near the N-terminus. In the motif sequence, R isarginine, W is tryptophan, and “(×)8” represent 8 amino acid residuesbetween R and W. The RR(×)8W motif is generally found in the N-terminalpart of class III terpene synthase proteins. The amino acid sequence ofSEQ ID NO: 2 includes four amino acid residues, MVEP, to the N-terminusof the RR(×)8W motif. One or more of these MVEP amino acid residues maynot necessarily affect the myrcene synthase function or its expressionin genetically modified microbial host cells. Thus, in certainembodiments, a myrcene synthase variant may further include a deletionof one or more amino acid residues of MVEP at the N-terminus of SEQ IDNO: 2.

In other embodiments, a myrcene synthase variant may include one or moreamino acid substitutions compared to a reference sequence. For example,a myrcene synthase variant may include one, two, three, four, five, six,seven, eight, nine, ten, or more amino acid substitutions compared tothe reference myrcene synthase sequence, and retains the myrcenesynthase activity of the reference sequence. In certain embodiments, amyrcene synthase variant comprises one or more amino acid substitutionsup to 5%, up to 10%, up to 15%, up to 20%, up to 25%, or up to 30% ofthe reference myrcene synthase sequence. In certain embodiments, aminoacid substitutions may include conservative amino acid substitutions.For example, a basic amino acid residue (e.g., lysine) in the referencemyrcene synthase may be exchanged with another basic amino acid residue(e.g., arginine). In another example, a polar amino acid residue (e.g.,serine) in the reference myrcene synthase may be substituted withanother polar amino acid residue (e.g., threonine). In otherembodiments, amino acid substitutions may include non-conservative aminoacid substitutions. For example, a nonpolar amino acid residue (e.g.,glycine) in the reference myrcene synthase may be substituted with anacidic amino acid residue (e.g., glutamine). In another example, anaromatic amino acid residue (e.g., tyrosine) may be substituted with acyclic amino acid residue (e.g., proline).

In certain embodiments, a myrcene synthase variant comprises an aminoacid sequence that has at least about 70%, at least about 75%, at leastabout 80%, at least about 85%, at least about 90%, at least about 95%,at least about 96%, at least about 97%, at least about 98%, or at leastabout 99% sequence identity to a reference myrcene synthase. In anembodiment, the reference myrcene synthase comprises an amino acidsequence of SEQ ID NO: 2, the wild-type sequence of Ocimum basilicummyrcene synthase. Thus, in certain embodiments, a myrcene synthasevariant comprises an amino acid sequence that has at least about 70%, atleast about 75%, at least about 80%, at least about 85%, at least about90%, at least about 95%, at least about 96%, at least about 97%, atleast about 98%, or at least about 99% sequence identity to SEQ ID NO:2.

In certain embodiments, myrcene synthase variants are not naturallyoccurring myrcene synthases, and comprise one or more amino acidsubstitutions compared to wild-type myrcene synthases. In certainembodiments, a myrcene synthase variant may comprise at least onevariant amino acid residue compared to SEQ ID NO: 2 at one or more ofpositions 27, 28, 207, 213, 222, 342, 347, 381, 382, 389, 390, 401, 404,428, 439, 466, 482, 484, 505, 514, 517, 524, 527, 528, 543, 544, and552, wherein the positions are numbered with reference to SEQ ID NO: 2.As shown in the examples section, one or more amino acid substitutionsat these positions of SEQ ID NO: 2 generated beneficial mutations interms of improving in vivo myrcene synthase activity or performance. Forexample, as described in Example 7.9, myrcene synthase variantscomprising one or more mutations at these positions of SEQ ID NO: 2exhibited an improved myrcene to limonene production ratio in acompetition assay. In another example, as described in Example 7.11,myrcene synthase variants comprising one or more mutations at thesepositions of SEQ ID NO: 2 exhibited improved myrcene production (e.g.,titer) compared to a parent myrcene synthase comprising an amino acidsequence of SEQ ID NO: 2.

In certain embodiments, the myrcene synthase variants described hereincomprise one or more amino acid substitutions at certain amino acidpositions, relative to the Ocimum basilicum myrcene synthase of SEQ IDNO: 2. However, corresponding positions in homologs or orthologs of theOcimum basilicum myrcene synthase can be readily determined by sequencealignment algorithms known in the art, and the amino acid substitutionsdescribed with reference to positions of SEQ ID NO: 2 may be applied tothe homologs or orthologs of the Ocimum basilicum myrcene synthase(e.g., O. campechianum, O. tenuiflorum, O. centraliafricanum, and thelike). While SEQ ID NO: 2 is derived from Ocimum basilicum, it isexpected that other Ocimum species myrcene synthases or other homologousmyrcene synthases may share a substantial sequence identity (e.g., atleast 50%). The homologous myrcene synthases of Ocimum basilicum myrcenesynthase may also hybridize under stringent conditions to the complementof a nucleic acid sequence encoding SEQ ID NO: 2 (e.g., a nucleotidesequence of SEQ ID NO: 1). The amino acid substitutions at one or morepositions relative to SEQ ID NO: 2 may be incorporated into other Ocimumspecies myrcene synthases or other homologous sequences (e.g., having atleast 70%, 80%, 90%, or 95% sequence identity to SEQ ID NO: 2) togenerate additional myrcene synthase variants which retain or possessimproved myrcene synthase activity compared to the parent myrcenesynthase.

Thus, in certain embodiments, a myrcene synthase variant comprises anamino acid sequence that has at least about 70%, at least about 75%, atleast about 80%, at least about 85%, at least about 90%, at least about95%, at least about 96%, at least about 97%, at least about 98%, or atleast about 99% sequence identity to SEQ ID NO: 2, and comprises one ormore variant amino acid residues compared to SEQ ID NO: 2 at one or morepositions selected from the group consisting of positions 27, 28, 207,213, 222, 342, 347, 381, 382, 389, 390, 401, 404, 428, 439, 466, 482,484, 505, 514, 517, 524, 527, 528, 543, 544, and 552, wherein thepositions are numbered with reference to SEQ ID NO: 2.

In other embodiments, a myrcene synthase variant comprises an amino acidsequence that is encoded by a nucleic acid molecule that hybridizesunder stringent hybridization conditions to the complement of SEQ ID NO:1, and comprises one or more variant amino acid residues compared to SEQID NO: 2 at one or more positions selected from the group consisting ofpositions 27, 28, 207, 213, 222, 342, 347, 381, 382, 389, 390, 401, 404,428, 439, 466, 482, 484, 505, 514, 517, 524, 527, 528, 543, 544, and552, wherein the positions are numbered with reference to SEQ ID NO: 2.In some embodiments, a myrcene synthase variant is encoded by a nucleicacid molecule that hybridizes under stringent conditions to thecomplement of SEQ ID NO: 3 and comprises at least one variant amino acidresidue compared to SEQ ID NO: 2 at one or more positions selected fromthe group consisting of positions 27, 28, 207, 213, 222, 342, 347, 381,382, 389, 390, 401, 404, 428, 439, 466, 482, 484, 505, 514, 517, 524,527, 528, 543, 544, and 552, wherein the positions are numbered withreference to SEQ ID NO: 2. The nucleotide sequence of SEQ ID NO: 3encodes the amino acid sequence of SEQ ID ON: 2 and is a codon optimizedversion of SEQ ID NO: 1 for expression in yeast host cells (e.g., S.cerevisiae).

In certain embodiments, the myrcene synthase variant has an amino acidsequence shown in SEQ ID NO: 2 but comprises a histidine to isoleucinesubstitution at position 27 (H27I). In certain embodiments, the myrcenesynthase variant has an amino acid sequence shown in SEQ ID NO: 2 butcomprises a histidine to cysteine substitution at position 27 (H27C). Incertain embodiments, the myrcene synthase variant has an amino acidsequence shown in SEQ ID NO: 2 but comprises a serine to histidinesubstitution at position 28 (S28H). In certain embodiments, the myrcenesynthase variant has an amino acid sequence shown in SEQ ID NO: 2 butcomprises an isoleucine to valine substitution at position 207 (I207V).In certain embodiments, the myrcene synthase variant has an amino acidsequence shown in SEQ ID NO: 2 but comprises a lysine to cysteinesubstitution at position 213 (K213C). In certain embodiments, themyrcene synthase variant has an amino acid sequence shown in SEQ ID NO:2 but comprises a lysine to histidine substitution at position 213(K213H). In certain embodiments, the myrcene synthase variant has anamino acid sequence shown in SEQ ID NO: 2 but comprises a lysine toarginine substitution at position 213 (K213R). In certain embodiments,the myrcene synthase variant has an amino acid sequence shown in SEQ IDNO: 2 but comprises a lysine to valine substitution at position 213(K213V). In certain embodiments, the myrcene synthase variant has anamino acid sequence shown in SEQ ID NO: 2 but comprises an arginine toasparagine substitution at position 222 (R222N). In certain embodiments,the myrcene synthase variant has an amino acid sequence shown in SEQ IDNO: 2 but comprises a cysteine to leucine substitution at position 342(C342L). In certain embodiments, the myrcene synthase variant has anamino acid sequence shown in SEQ ID NO: 2 but comprises a tyrosine toarginine substitution (Y347R). In certain embodiments, the myrcenesynthase variant has an amino acid sequence shown in SEQ ID NO: 2 butcomprises a phenylalanine to leucine substitution at position 381(F381L). In certain embodiments, the myrcene synthase variant has anamino acid sequence shown in SEQ ID NO: 2 but comprises a valine toleucine substitution at position 382 (V382L). In certain embodiments,the myrcene synthase variant has an amino acid sequence shown in SEQ IDNO: 2 but comprises an aspartic acid to glycine substitution at position389 (D389G). In certain embodiments, the myrcene synthase variant has anamino acid sequence shown in SEQ ID NO: 2 but comprises an aspartic acidto serine substitution at position 389 (D389S). In certain embodiments,the myrcene synthase variant has an amino acid sequence shown in SEQ IDNO: 2 but comprises a glycine to aspartic acid substitution at position390 (G390D). In certain embodiments, the myrcene synthase variant has anamino acid sequence shown in SEQ ID NO: 2 but comprises an asparagine toisoleucine substitution at position 401 (N401I). In certain embodiments,the myrcene synthase variant has an amino acid sequence shown in SEQ IDNO: 2 but comprises an asparagine to valine substitution at position 401(N401V). In certain embodiments, the myrcene synthase variant has anamino acid sequence shown in SEQ ID NO: 2 but comprises an isoleucine tovaline substitution at position 404 (I404V). In certain embodiments, themyrcene synthase variant has an amino acid sequence shown in SEQ ID NO:2 but comprises a valine to leucine substitution at position 428(V428L). In certain embodiments, the myrcene synthase variant has anamino acid sequence shown in SEQ ID NO: 2 but comprises a tyrosine toleucine substitution at position 439 (Y439L). In certain embodiments,the myrcene synthase variant has an amino acid sequence shown in SEQ IDNO: 2 but comprises an alanine to cysteine substitution at position 466(A466C). In certain embodiments, the myrcene synthase variant has anamino acid sequence shown in SEQ ID NO: 2 but comprises an alanine toserine substitution at position 466 (A466S). In certain embodiments, themyrcene synthase variant has an amino acid sequence shown in SEQ ID NO:2 but comprises an arginine to cysteine substitution at position 482(R482C). In certain embodiments, the myrcene synthase variant has anamino acid sequence shown in SEQ ID NO: 2 but comprises an arginine toaspartic acid substitution at position 482 (R482D). In certainembodiments, the myrcene synthase variant has an amino acid sequenceshown in SEQ ID NO: 2 but comprises an arginine to histidinesubstitution at position 482 (R482H). In certain embodiments, themyrcene synthase variant has an amino acid sequence shown in SEQ ID NO:2 but comprises an arginine to isoleucine substitution at position 482(R482I). In certain embodiments, the myrcene synthase variant has anamino acid sequence shown in SEQ ID NO: 2 but comprises an arginine toleucine substitution at position 482 (R482L). In certain embodiments,the myrcene synthase variant has an amino acid sequence shown in SEQ IDNO: 2 but comprises an arginine to asparagine substitution at position482 (R482N). In certain embodiments, the myrcene synthase variant has anamino acid sequence shown in SEQ ID NO: 2 but comprises an arginine tovaline substitution (R482V). In certain embodiments, the myrcenesynthase variant has an amino acid sequence shown in SEQ ID NO: 2 butcomprises a histidine to tyrosine substitution at position 484 (H484Y).In certain embodiments, the myrcene synthase variant has an amino acidsequence shown in SEQ ID NO: 2 but comprises a cysteine to isoleucinesubstitution at position 505 (C505I). In certain embodiments, themyrcene synthase variant has an amino acid sequence shown in SEQ ID NO:2 but comprises a cysteine to leucine substitution at position 505(C505L). In certain embodiments, the myrcene synthase variant has anamino acid sequence shown in SEQ ID NO: 2 but comprises a cysteine tovaline substitution (C505V). In certain embodiments, the myrcenesynthase variant has an amino acid sequence shown in SEQ ID NO: 2 butcomprises a glycine to leucine substitution at position 514 (G514L). Incertain embodiments, the myrcene synthase variant has an amino acidsequence shown in SEQ ID NO: 2 but comprises a glycine to valinesubstitution at position 514 (G514V). In certain embodiments, themyrcene synthase variant has an amino acid sequence shown in SEQ ID NO:2 but comprises a serine to glycine substitution at position 517(S517G). In certain embodiments, the myrcene synthase variant has anamino acid sequence shown in SEQ ID NO: 2 but comprises a phenylalanineto leucine substitution at position 524 (F524L). In certain embodiments,the myrcene synthase variant has an amino acid sequence shown in SEQ IDNO: 2 but comprises a phenylalanine to valine substitution at position524 (F524V). In certain embodiments, the myrcene synthase variant has anamino acid sequence shown in SEQ ID NO: 2 but comprises a valine tocysteine substitution at position 527 (V527C). In certain embodiments,the myrcene synthase variant has an amino acid sequence shown in SEQ IDNO: 2 but comprises a valine to phenylalanine substitution at position527 (V527F). In certain embodiments, the myrcene synthase variant has anamino acid sequence shown in SEQ ID NO: 2 but comprises a valine tohistidine substitution at position 527 (V527H). In certain embodiments,the myrcene synthase variant has an amino acid sequence shown in SEQ IDNO: 2 but comprises a valine to leucine substitution at position 527(V527L). In certain embodiments, the myrcene synthase variant has anamino acid sequence shown in SEQ ID NO: 2 but comprises a valine toasparagine substitution at position 527 (V527N). In certain embodiments,the myrcene synthase variant has an amino acid sequence shown in SEQ IDNO: 2 but comprises a valine to serine substitution at position 527(V527S). In certain embodiments, the myrcene synthase variant has anamino acid sequence shown in SEQ ID NO: 2 but comprises a valine totyrosine substitution at position 527 (V527Y). In certain embodiments,the myrcene synthase variant has an amino acid sequence shown in SEQ IDNO: 2 but comprises a glutamic acid to aspartic acid substitution atposition 528 (E528D). In certain embodiments, the myrcene synthasevariant has an amino acid sequence shown in SEQ ID NO: 2 but comprises amethionine to isoleucine substitution at position 543 (M543I). Incertain embodiments, the myrcene synthase variant has an amino acidsequence shown in SEQ ID NO: 2 but comprises an alanine to serinesubstitution at position 544 (A544S). In certain embodiments, themyrcene synthase variant has an amino acid sequence shown in SEQ ID NO:2 but comprises a glutamine to arginine substitution at position 552(Q552R). In certain embodiments, the myrcene synthase variant has anycombination of amino acid substitutions described herein.

In certain embodiments, provided herein are myrcene synthase variantswhich comprise an amino acid sequence that has at least about 70%, atleast about 75%, at least about 80%, at least about 85%, at least about90%, at least about 95%, at least about 96%, at least about 97%, atleast about 98%, or at least about 99% sequence identity to SEQ ID NO: 2and comprises at least one variant amino acid residue compared to SEQ IDNO: 2, wherein at least one variant amino acid residue is selected fromthe group consisting of H27I, H27C, S28H, I207V, K213C, K213H, K213R,K213V, R222N, C342L, Y347R, F381L, V382L, D389G, D389S, G390D, N401I,N401V, I404V, V428L, Y439L, A466C, A466S, R482C, R482D, R482H, R482I,R482L, R482N, R482V, H484Y, C505I, C505L, C505V, G514L, G514V, S517G,F524L, F524V, V527C, V527F, V527H, V527L, V527N, V527S, V527Y, E528D,M543I, A544S, and Q552R, wherein the position of amino acid residue isnumbered with reference to SEQ ID NO: 2.

In certain embodiments, provided herein are myrcene synthase variantswhich are encoded by a nucleic acid molecule that hybridizes understringent conditions to the complement of SEQ ID NO: 1, SEQ ID NO: 3, orSEQ ID NO: 4 and comprises at least one variant amino acid residuecompared to SEQ ID NO: 2, wherein at least one variant amino acidresidues selected from the group consisting of H27I, H27C, S28H, I207V,K213C, K213H, K213R, K213V, R222N, C342L, Y347R, F381L, V382L, D389G,D389S, G390D, N401I, N401V, I404V, V428L, Y439L, A466C, A466S, R482C,R482D, R482H, R482I, R482L, R482N, R482V, H484Y, C505I, C505L, C505V,G514L, G514V, S517G, F524L, F524V, V527C, V527F, V527H, V527L, V527N,V527S, V527Y, E528D, M543I, A544S, and Q552R, wherein the position ofamino acid residue is numbered with reference to SEQ ID NO: 2.

In certain embodiments, a myrcene synthase variant comprises one variantamino acid residue compared to SEQ ID NO: 2. In certain embodiments, amyrcene synthase variant comprises two variant amino acid residuescompared to SEQ ID NO: 2. In certain embodiments, a myrcene synthasevariant comprises three variant amino acid residues compared to SEQ IDNO: 2. In certain embodiments, a variant myrcene synthase comprises fourvariant amino acid residues compared to SEQ ID NO: 2. In certainembodiments, a myrcene synthase variant comprises five variant aminoacid residues compared to SEQ ID NO: 2. In certain embodiments, amyrcene synthase variant comprises at least 6, 7, 8, 9, 10, 11, 12, 13,14, 15, 16, 17, 18, 19, 20, or more amino acid substitutions compared toSEQ ID NO: 2.

In certain embodiments, a myrcene synthase variant comprises at leastone set of variant amino acid residues compared to SEQ ID NO: 2, andwherein the at least one set of variant amino acid residues is selectedfrom the group of sets of variant amino acid residues consisting of: (a)F381L, I404V, E528D, and M543I; (b) I404V and E528D; (c) F381L, D389G,I404V, Y439L, and E528D; (d) F381L, E528D, and M543I; (e) F381L, I404V,and E528D; (f) F381L, I404V, E528D, and A544S; and (g) F381L, I404V,E528D, and Q552R, wherein the position is numbered with reference to SEQID NO: 2. As described in the examples section, each of these sets ofvariant amino acid residues, when introduced into the background of SEQID NO: 2, further improves the myrcene synthase activity relative to thereference myrcene synthase comprising SEQ ID NO: 2. One or more of thesesets of variant amino acid residues may also be introduced intohomologous sequences of SEQ ID NO: 2.

As described in the examples section, a myrcene synthase variant whichcomprises a set of variant amino acid residues F381L, I404V, and E528Dwas found to exhibit about a 14-fold increase in the myrcene synthaseactivity relative to the reference myrcene synthase comprising asequence of SEQ ID NO: 2, when encoded by the wild-type nucleotidesequence having SEQ ID NO: 1, in microbial host cells (e.g., S.cerevisiae). Thus, in certain embodiments, one or more variant aminoacid residues can be further introduced into this myrcene synthasevariant (referred to as “14×ObMS” variant) to generate additionalmyrcene synthase variants with improved myrcene synthase activities. Forexample, additional myrcene synthase variants may be generated byintroducing into the 14×ObMS variant, one or more variant amino acidresidues, such as H27I, H27C, S28H, I207V, K213C, K213H, K213R, K213V,R222N, C342L, Y347R, V382L, D389G, D389S, G390D, N401I, N401V, V428L,Y439L, A466C, A466S, R482C, R482D, R482H, R482I, R482L, R482N, R482V,H484Y, C505I, C505L, C505V, G514L, G514V, S517G, F524L, F524V, V527C,V527F, V527H, V527L, V527N, V527S, V527Y, M543I, A544S, and Q552R.

In addition to specific amino acid substitutions described herein, othervariations of amino acid substitutions, deletions, additions, andinsertions in the reference myrcene synthases are within the scope ofthe present invention. The function of these myrcene synthase variantscan be readily determined by expressing each variant in microbial hostcells and measuring production of myrcene using plate assays, headspaceassays, competition assays, and GC techniques described in the examplessection or other suitable techniques known in the art.

As shown in the examples section, the amino acid substitutions inmyrcene synthase variants described herein change in vivo performance ofthe reference myrcene synthase, that is, their ability to convert ageranyl pyrophosphate substrate to a myrcene when expressed in microbialhost cells. Without wishing to be bound by any theory, changes in invivo performance of myrcene synthase variants may be due to changes inbinding affinity for substrates, enzyme kinetics, transcription, proteinexpression level, protein stability, and the like. In certainembodiments, myrcene synthase variants may also alter substrateutilization or monoterpene product distribution.

In certain embodiments, changes in in vivo performance of myrcenesynthase variants can be assessed by measuring and comparing myrceneproduction with that of a reference myrcene synthase (e.g., wild-typemyrcene synthase of Ocimum basilicum) under the same culture conditions.The myrcene production can be measured in terms of titer, yield and/orproductivity using any suitable techniques known in the art. Forexample, the myrcene production can be measured using culture conditionsand myrcene titer analysis techniques described in the examples section.

In certain embodiments, the myrcene production by a myrcene synthasevariant, when expressed in genetically modified microbial host cells, isat least 10%, at least about 15%, at least about 20%, at least about25%, at least about 30%, at least about 35%, at least about 40%, atleast about 45%, at least about 50%, at least about 60%, at least about70%, at least about 80%, at least about 90%, at least about 2-fold, atleast about 2.5-fold, at least about 5-fold, at least about 10-fold, atleast about 20-fold, at least about 30-fold, at least about 40-fold, atleast about 50-fold, at least about 75-fold, at least about 100-foldhigher than the myrcene production by a reference myrcene synthase. Incertain embodiments, the fold increase in myrcene production by amyrcene synthase variant is compared to the myrcene production by thereference myrcene synthase, wherein the reference myrcene synthasecomprises SEQ ID NO: 2 which is encoded by SEQ ID NO: 1. In anembodiment, the myrcene production is measured using GC techniquesdescribed in Examples 6.4 and 6.5 in the examples section. The myrceneproduction is compared between the variant and reference myrcenesynthases under equivalent experimental conditions (e.g., host cell,control sequences, culture conditions, and the like).

In other embodiments, changes in in vivo performance of myrcene synthasevariants can be assessed by measuring myrcene titer and a comparisonmonoterpene titer in a competition assay. An illustrative example of acompetition assay employs a known monoterpene synthase (e.g., a limonenesynthase) as the comparison enzyme against which myrcene synthasevariants are compared. Both the comparison monoterpene synthase and eachof the myrcene synthase variants are co-expressed in a microbial hostcell in which they then compete for the same substrate (e.g., geranylpyrophosphate) to produce their corresponding monoterpenes. Since theperformance of the comparison enzyme remains constant in the geneticallymodified microbial host cells, any changes in the ratios of titers ofthe monoterpenes produced by the test myrcene synthase variant and thecomparison monoterpene synthase are the direct result of the activitiesof the myrcene synthase variants. For example, if a limonene synthase isused as the comparison enzyme, then the ratios of titers of myrcene andlimonene can be measured for each myrcene synthase variant.Consequently, such ratios can be used to identify myrcene synthasevariants with improved in vivo performance, and/or to quantitativelycompare the myrcene synthase variants for their in vivo kineticcapacities in diverting geranyl pyrophosphate to the production ofmyrcene. An exemplary competition assay that is suitable for use inscreening is further described in the examples section.

In certain embodiments, myrcene synthase variants exhibit improvedratios of titer of myrcene and a comparison monoterpene synthase (e.g.,limonene synthase) by at least 5%, at least 10%, at least about 15%, atleast about 20%, at least about 25%, at least about 30%, at least about35%, at least about 40%, at least about 45%, at least about 50%, atleast about 60%, at least about 70%, at least about 80%, at least about90%, at least about 2-fold, at least about 2.5-fold, at least about5-fold, at least about 10-fold, at least about 20-fold, at least about30-fold, at least about 40-fold, at least about 50-fold, at least about75-fold, at least about 100-fold than the ratio of titer of myrcene andcomparison monoterpene (e.g., limonene) produced by a reference myrcenesynthase (e.g., wild-type myrcene synthase comprising SEQ ID NO: 2 whichis encoded by SEQ ID NO: 1).

In certain embodiments, an additional assay may be performed todetermine whether a myrcene synthase variant has retained or improvedthe monoterpene product profile by comparing the product profile of themyrcene synthase variant with that of a reference myrcene synthase. Asshown in Example 7.7, the wild-type myrcene synthase comprising SEQ IDNO: 2, when expressed in genetically modified microbial host cells,produces between about 89% to 92% myrcene compared to the total amountof monoterpenes produced by the genetically modified microbial hostcells. It may be desirable to screen for myrcene synthase variants whichare capable of producing myrcene at even a higher proportion, forexample, at least about 93%, 94%, 95%, 96%, 97%, 98%, or 99% myrcene,compared to the wild-type myrcene synthase comprising SEQ ID NO: 2. GCtechniques described in the example section can be used to determinewhether a myrcene synthase variant has at least retained its monoterpeneproduct profile or improved its product profile by increasing theproportion of myrcene in the monoterpenes produced by the geneticallymodified microbial host cells.

The assays described above are merely exemplary, and other suitableassays to determine in vivo performance of myrcene synthase variantsapparent to those skilled in the art may be utilized to screen myrcenesynthase variants with improved in vivo performance.

7.3.2. Myrcene Synthase Variant Nucleic Acid Sequences

In another aspect, provided herein are isolated nucleic acid moleculesthat encode myrcene synthases described herein. In certain embodiments,the isolated nucleic acid molecules may comprise nucleotidesubstitutions, deletions, additions, and/or insertions to SEQ ID NO: 1,which may or may not result in changes in the corresponding amino acidsequences. In certain embodiments, the isolated nucleic acid moleculesmay comprise nucleotide substitutions, deletions, additions, and/orinsertions into homologous sequences of SEQ ID NO: 1 which encodemyrcene synthases. In certain embodiments, modifications to the isolatednucleic acid molecules may be silent due to degeneracy of the geneticcode, and the protein encoded by the variant is identical to the proteinencoded by the reference nucleotide sequence. In certain embodiments,modifications to the isolated nucleic acid molecules may causesubstitutions of amino acids in the protein encoded by the variantcompared to the protein encoded by the reference nucleotide sequence.

In some embodiments where nucleotide changes do not result in changes tothe amino acid sequence, the changes may nonetheless result in improvedactivity of the myrcene synthase, for example, through codonoptimization. The codons for nucleic acid molecules encoding myrcenesynthases can be optimized for any selected microbial host cell. In someembodiments, the nucleotide sequence encoding the myrcene synthase isaltered to reflect the codon preferences of Saccharomyces cerevisiae(see, e.g., Bennetzen and Hall (1982) J. Biol. Chem. 257(6): 3026-3031).In some embodiments, the nucleotide sequence encoding the myrcenesynthase is altered to reflect the codon preferences for Escherichiacoli (see, e.g., Gouy and Gautier (1982) Nucleic Acids Res.10(22):7055-7074; Eyre-Walker (1996) Mol. Biol. Evol. 13(6):864-872;Nakamura et al. (2000) Nucleic Acids Res. 28(1):292). Codon optimizationfor other microbial host cells can be readily determined using codonusage tables or can be performed using commercially available software,such as CodonOp (https://www.idtdna.com/CodonOptfrom) from IntegratedDNA Technologies.

In one embodiment, provided herein is an isolated nucleic acid moleculecomprising the nucleotide sequence shown in SEQ ID NO: 3. The nucleotidesequence of SEQ ID NO: 3 includes distinct codon optimizations forexpression in yeast host cells (e.g., S. cerevisiae). The nucleotidesequence having SEQ ID NO: 3 is referred to as the 5×ObMS variantnucleotide sequence. In certain embodiments, when the 5×ObMS isexpressed in genetically modified microbial host cells, it exhibitsabout a five-fold increase in myrcene synthase activity compared to the1×ObMS (wild-type O. basilicum mycene synthase nucleic acid moleculecomprising SEQ ID NO: 1, which is not codon optimized) in a competitionassay as described in the examples section. The codon optimizednucleotide sequence shown in SEQ ID NO: 3 for yeast host cells is merelyexemplary, and other codon optimized nucleotide sequences for yeast orother microbial host cells can be generated using codon usage tables orcodon optimizing software.

In certain embodiments, provided herein are isolated nucleic acidmolecules that encode variant myrcene synthases described above. Forinstance, isolated nucleic acid molecules encode myrcene synthasevariants which comprise an amino acid sequence that has at least about70%, at least about 75%, at least about 80%, at least about 85%, atleast about 90%, at least about 95%, at least about 96%, at least about97%, at least about 98%, or at least about 99% sequence identity to SEQID NO: 2. In certain embodiments, isolated nucleic acid molecules encodemyrcene synthase variants comprising an amino acid sequence that has atleast about 70%, at least about 75%, at least about 80%, at least about85%, at least about 90%, at least about 95%, at least about 96%, atleast about 97%, at least about 98%, or at least about 99% sequenceidentity to SEQ ID NO: 2, and comprises at least one variant amino acidresidue compared to SEQ ID NO: 2 at one or more of positions selectedfrom the group consisting of 27, 28, 207, 213, 222, 342, 347, 381, 382,389, 390, 401, 404, 428, 439, 466, 482, 484, 505, 514, 517, 524, 527,528, 543, 544, and 552, wherein the positions are numbered withreference to SEQ ID NO: 2. In certain embodiments, the isolated nucleicacid molecules encoding myrcene synthase variants are not naturallyoccurring nucleic acid molecules.

In certain embodiments, provided herein are isolated nucleic acidmolecules that hybridize under stringent conditions to the complement ofSEQ ID NO: 1 and encode myrcene synthase variants comprising at leastone variant amino acid residue compared to SEQ ID NO: 2 at one or moreof positions selected from the group consisting of 27, 28, 207, 213,222, 342, 347, 381, 382, 389, 390, 401, 404, 428, 439, 466, 482, 484,505, 514, 517, 524, 527, 528, 543, 544, and 552, wherein the positionsare numbered with reference to SEQ ID NO: 2. In certain embodiments,provided herein are isolated nucleic acid molecules that hybridize understringent conditions to the complement of SEQ ID NO: 3 and encodes amyrcene synthase variant comprising at least one variant amino acidresidue compared to SEQ ID NO: 2 at one or more of positions selectedfrom the group consisting of 27, 28, 207, 213, 222, 342, 347, 381, 382,389, 390, 401, 404, 428, 439, 466, 482, 484, 505, 514, 517, 524, 527,528, 543, 544, and 552, wherein the positions are numbered withreference to SEQ ID NO: 2. As described above, the nucleotide sequenceof SEQ ID NO: 3 encodes the amino acid sequence of SEQ ID ON: 2 and is acodon optimized version of SEQ ID NO: 1 for expression in yeast hostcells (e.g., S. cerevisiae). In certain embodiments, provided herein areisolated nucleic acid molecules that hybridize under stringentconditions to the complement of SEQ ID NO: 4 and encodes a myrcenesynthase variant comprising at least one variant amino acid residuecompared to SEQ ID NO: 2 at one or more of positions selected from thegroup consisting of 27, 28, 207, 213, 222, 342, 347, 381, 382, 389, 390,401, 404, 428, 439, 466, 482, 484, 505, 514, 517, 524, 527, 528, 543,544, and 552, wherein the positions are numbered with reference to SEQID NO: 2. The nucleotide sequence of SEQ ID NO: 4 encodes the amino acidsequence of SEQ ID NO: 2 with three amino acid substitutions F381L,I404V, and E528D, wherein the positions are numbered with reference toSEQ ID NO: 2.

In certain embodiments, provided herein are isolated nucleic acidmolecules encoding myrcene synthase variants which comprise an aminoacid sequence that has at least about 70%, at least about 75%, at leastabout 80%, at least about 85%, at least about 90%, at least about 95%,at least about 96%, at least about 97%, at least about 98%, or at leastabout 99% sequence identity to SEQ ID NO: 2 and comprises at least onevariant amino acid residue compared to SEQ ID NO: 2, wherein at leastone variant amino acid residue is selected from the group consisting ofH27I, H27C, S28H, I207V, K213C, K213H, K213R, K213V, R222N, C342L,Y347R, F381L, V382L, D389G, D389S, G390D, N401I, N401V, I404V, V428L,Y439L, A466C, A466S, R482C, R482D, R482H, R482I, R482L, R482N, R482V,H484Y, C505I, C505L, C505V, G514L, G514V, S517G, F524L, F524V, V527C,V527F, V527H, V527L, V527N, V527S, V527Y, E528D, M543I, A544S, andQ552R, wherein the positions are numbered with reference to SEQ ID NO:2. In certain embodiments, provided herein are isolated nucleic acidmolecules that hybridize under stringent conditions to the complement ofSEQ ID NOS: 1, 3, or 4, and encode myrcene synthase variants comprisingat least one variant amino acid residue compared to SEQ ID NO: 2,wherein at least one variant amino acid residue is selected from thegroup consisting of H27I, H27C, S28H, I207V, K213C, K213H, K213R, K213V,R222N, C342L, Y347R, F381L, V382L, D389G, D389S, G390D, N401I, N401V,I404V, V428L, Y439L, A466C, A466S, R482C, R482D, R482H, R482I, R482L,R482N, R482V, H484Y, C505I, C505L, C505V, G514L, G514V, S517G, F524L,F524V, V527C, V527F, V527H, V527L, V527N, V527S, V527Y, E528D, M543I,A544S, and Q552R, wherein the positions are numbered with reference toSEQ ID NO: 2.

In certain embodiments, provided herein are isolated nucleic acidmolecules encoding myrcene synthase variants which comprise at least oneset of variant amino acid residues compared to SEQ ID NO: 2, wherein atleast one set of variant amino acid residues is selected from the groupof sets of variant amino acid residues consisting of: (a) F381L, I404V,E528D, and M543I; (b) I404V and E528D; (c) F381L, D389G, I404V, Y439L,and E528D; (d) F381L, E528D, and M543I; (e) F381L, I404V, and E528D; (f)F381L, I404V, E528D, and A544S; and (g) F381L, I404V, E528D, and Q552R,wherein the positions are numbered with reference to SEQ ID NO: 2. Incertain embodiments, provided herein are isolated nucleic acid moleculesthat hybridize under stringent conditions to the complement of SEQ IDNOS: 1, 3, or 4, and encode myrcene synthase variants comprising atleast one set of variant amino acid residues compared to SEQ ID NO: 2,and wherein at least one set of variant amino acid residues is selectedfrom the group of sets of variant amino acid residues consisting of: (a)F381L, I404V, E528D, and M543I; (b) I404V and E528D; (c) F381L, D389G,I404V, Y439L, and E528D; (d) F381L, E528D, and M543I; (e) F381L, I404V,and E528D; (f) F381L, I404V, E528D, and A544S; and (g) F381L, I404V,E528D, and Q552R, wherein the positions are numbered with reference toSEQ ID NO: 2.

In certain embodiments, isolated nucleic acid molecules encoding myrcenesynthase variants may be generated using the nucleotide sequence havingSEQ ID NO: 3 (which is codon optimized) as a background nucleotidesequence for replacing specific codons to encode a variant myrcenesynthase. For example, SEQ ID NO: 4 is generated by using SEQ ID NO: 3as the background nucleotide sequence with three codons replaced toencode a myrcene synthase variant comprising three variant amino acidresidues F381L, I404V, and E528D compared to SEQ ID NO: 2, wherein thepositions are numbered with reference to SEQ ID NO: 2. As described inthe examples section, when the nucleic acid molecule comprising thesequence of SEQ ID NO: 4 was expressed in genetically modified microbialhost cells, it was discovered that this myrcene synthase variant (alsoreferred to as the 14×ObMS) exhibited about a 14-fold increase in themyrcene synthase activity compared to genetically modified microbialhost cells expressing wild-type myrcene synthase encoded by a nucleicacid sequence comprising SEQ ID NO: 1.

Additional myrcene synthase variant nucleic acid molecules can beproduced using any suitable genetic engineering techniques known in theart. These techniques include, for example, error-prone PCR, shuffling,oligonucleotide-directed mutagenesis, assembly PCR, site-specificmutagenesis, cassette mutagenesis, and the like. Furthermore,combinatorial libraries based on saturation mutagenesis may be generatedto engineer additional myrcene synthase variant nucleic acid moleculesthat result in enhanced in vivo performance of myrcene synthases.

7.4 Other Enzymes for Co-Expression with Myrcene Synthase forBiosynthesis of Myrcene

In another aspect, the myrcene synthases described herein can beco-expressed with other enzymes for biosynthesis of myrcene in microbialhost cells. In some embodiments, in addition to a heterologous nucleicacid molecule encoding a myrcene synthase, microbial host cells can begenetically modified to include heterologous nucleic acid moleculesencoding one or more enzymes of the MEV pathway. In other embodiments,in addition to a heterologous nucleic acid molecule encoding a myrcenesynthase, microbial host cells can be genetically modified to includeone or more heterologous nucleic acid molecules encoding one or moreenzymes of the DXP pathway. In another embodiment, in addition to aheterologous nucleic acid molecule encoding a myrcene synthase,microbial host cells can be genetically modified to comprise aheterologous nucleic acid molecule encoding a geranyl pyrophosphatesynthase. In yet another embodiment, the microbial host cells can begenetically modified to include any combination of these and otherheterologous nucleic acid molecules.

7.4.1. Geranyl Pyrophosphate Synthase

In certain embodiments, a myrcene synthase provided herein isco-expressed with a geranyl pyrophosphate synthase (GPPS). A GPPS is anenzyme that can condense one molecule of isopentenyl pyrophosphate (IPP)with one molecule of dimethylallyl pyrophosphate (DMAPP) to form onemolecule of geranyl pyrophosphate (“GPP”). As shown in FIG. 1 , geranylpyrophosphate is a precursor for myrcene synthases. Thus, in someembodiments, a heterologous nucleic acid molecule encoding a geranylpyrophosphate synthase (GPPS) can be introduced together with aheterologous nucleic acid molecule encoding a myrcene synthase intomicrobial host cells to catalyze the formation of a GPP substrate forthe myrcene synthase. In some embodiments, the GPPS nucleotide sequencesmay be modified (e.g., codon optimized, truncated, mutagenized, and thelike) prior to co-expressing the GPPS sequence together with a myrcenesynthase sequence.

Illustrative examples of nucleotide sequences encoding such a GPPSinclude, but are not limited to: (AF513111; Abies grandis), (AF513112;AF513112.1 Abies grandis), (AF513113; Abies grandis), (AY534686;Antirrhinum majus), (AY534687; Antirrhinum majus), (AA82860; Antirrhinummajus), (AA82859; Antirrhinum majus), (ACQ90682; Humulus lupulus),(ACQ90681; Humulus lupulus) (Y17376; Arabidopsis thaliana), (AE016877,Locus API 1092; Bacillus cereus; ATCC 14579), (AJ243739; Citrussinensis), (AY534745; Clarkia breweri), (AY953508; Ips pini), (DQ286930;Lycopersicon esculentum), (AF182828; Mentha x piperita), (AF182827;Mentha x piperita), (MPI249453; Mentha x piperita), (PZE431697, LocusCAD24425; Paracoccus zeaxanthinmfaciens), (AY866498; Picrorhizakurrooa), (AY351862; Vitis vinifera), (AF203881, Locus AAF12843;Zymomonas mobilis), (ABS50454; Streptomyces culeolatus); (AAR08151;Vitis vinifera), and (JX417185; Catharanthus roseus), (JX417183;Catharanthus roseus), (JX417184; Catharanthus roseus), (AEZ55677; Salviamiltiorrhiza), (AEZ55681; Salvia miltiorrhiza), (AEZ55678; Salviamiltiorrhiza), (AFJ52721; Mangifera indica), (AFJ52722; Mangiferaindica), (GQ369788; Picea abies), (EU432047; Picea abies), (ABY90133;Glycine max), (AEL29573; Medicago sativa), (ABV71395; Phalaenopsisbellina), and (BAH90987; Oryza sativa subsp. japonica).

Among many of these known sequences, the present inventors found thatbacterial geranyl pyrophosphate synthase sequences, such as thosederived from Streptomyces aculeolatus, are particularly useful. Forexample, a codon optimized Streptomyces aculeolatus geranylpyrophosphate synthase (SaGPPS), when co-expressed with myrcenesynthases described herein, exhibits sufficient enzyme activity inmicrobial host cells to support normal strain growth and a relativelyhigh level of myrcene production. See, e.g., Example 7.8 for comparisonwith other GPPS sequences for myrcene production. Thus, in certainembodiments, the compositions and methods provided herein utilizebacterial geranyl pyrophosphate synthases, in particular SaGPPS, for theproduction of myrcene in microbial host cells. In an embodiment, SaGGPScomprising an amino acid sequence of SEQ ID NO: 7 or its homologoussequences may be used in the compositions and methods provided herein.In another embodiment, a codon optimized SaGPPS nucleic acid moleculecomprising the nucleotide sequence of SEQ ID NO: 6 may be used in thecompositions and methods provided herein.

7.4.2. MEV Pathway Enzymes

In some embodiments, the myrcene synthases provided herein areco-expressed with one or more heterologous nucleic acid moleculesencoding one or more mevalonate pathway enzymes in microbial host cells.FIG. 1 and FIG. 2A illustrate one example of the mevalonate pathway. Incertain embodiments, this biosynthetic pathway can be used ingenetically modified microbial host cells to provide sufficient carbonflow for the production of dimethylallyl pyrophosphate (DMAPP) andisopentenyl pyrophosphate (IPP), which, in turn, can be used forproduction of geranyl pyrophosphate and myrcene. Thus, in certainembodiments, the genetically modified microbial host cells comprise oneor more heterologous nucleic acid molecules encoding one or more enzymesof the mevalonate pathway, which effects increased production of myrceneas compared to a genetically unmodified parent cell.

In some embodiments, the myrcene producing microbial host cell can befurther genetically modified to comprise a heterologous nucleotidesequence encoding an enzyme that can condense two molecules ofacetyl-coenzyme A to form acetoacetyl-CoA, e.g., an acetyl-CoA thiolase.Illustrative examples of nucleotide sequences encoding such an enzymeinclude, but are not limited to: (NC_000913 REGION: 2324131.2325315;Escherichia coli), (D49362; Paracoccus denitrificans), and (L20428;Saccharomyces cerevisiae).

In some embodiments, the myrcene producing microbial host cell comprisesa heterologous nucleotide sequence encoding an enzyme that can condenseacetoacetyl-CoA with another molecule of acetyl-CoA to form3-hydroxy-3-methylglutaryl-CoA (HMG-CoA), e.g., a HMG-CoA synthase.Illustrative examples of nucleotide sequences encoding such an enzymeinclude, but are not limited to: (NC_001145. complement 19061.20536;Saccharomyces cerevisiae), (X96617; Saccharomyces cerevisiae), (X83882;Arabidopsis thaliana), (AB037907; Kitasatospora griseola), (BT007302;Homo sapiens), and (NC_002758, Locus tag SAV2546, GeneID 1122571;Staphylococcus aureus).

In some embodiments, the myrcene producing microbial host cell comprisesa heterologous nucleotide sequence encoding an enzyme that can convertHMG-CoA into mevalonate, e.g., a HMG-CoA reductase. Illustrativeexamples of nucleotide sequences encoding such an enzyme include, butare not limited to: (NM_206548; Drosophila melanogaster), (NC_002758,Locus tag SAV2545, GeneID 1122570; Staphylococcus aureus), (NM_204485;Gallus gallus), (AB015627; Streptomyces sp. KO 3988), (AF542543;Nicotiana attenuata), (AB037907; Kitasatospora griseola), (AX128213,providing the sequence encoding a truncated HMGR; Saccharomycescerevisiae), and (NC_001145: complement (115734.118898; Saccharomycescerevisiae).

In some embodiments, the myrcene producing microbial host cell comprisesa heterologous nucleotide sequence encoding an enzyme that can convertmevalonate into mevalonate 5-phosphate, e.g., a mevalonate kinase.Illustrative examples of nucleotide sequences encoding such an enzymeinclude, but are not limited to: (L77688; Arabidopsis thaliana), and(X55875; Saccharomyces cerevisiae).

In some embodiments, the myrcene producing microbial host cell comprisesa heterologous nucleotide sequence encoding an enzyme that can convertmevalonate 5-phosphate into mevalonate 5-pyrophosphate, e.g., aphosphomevalonate kinase. Illustrative examples of nucleotide sequencesencoding such an enzyme include, but are not limited to: (AF429385;Hevea brasiliensis), (NM_006556; Homo sapiens), and (NC_001145.complement 712315.713670; Saccharomyces cerevisiae).

In some embodiments, the myrcene producing microbial host cell comprisesa heterologous nucleotide sequence encoding an enzyme that can convertmevalonate 5-pyrophosphate into IPP, e.g., a mevalonate pyrophosphatedecarboxylase. Illustrative examples of nucleotide sequences encodingsuch an enzyme include, but are not limited to: (X97557; Saccharomycescerevisiae), (AF290095; Enterococcus faecium), and (U49260; Homosapiens).

In some embodiments, the myrcene producing microbial host cell comprisesone or more heterologous nucleotide sequences encoding more than oneenzyme of the MEV pathway. In some embodiments, the myrcene producingmicrobial host cell comprises one or more heterologous nucleotidesequences encoding two enzymes of the MEV pathway. In some embodiments,the myrcene producing microbial host cell comprises one or moreheterologous nucleotide sequences encoding an enzyme that can convertHMG-CoA into mevalonate and an enzyme that can convert mevalonate intomevalonate 5-phosphate. In some embodiments, the myrcene producingmicrobial host cell comprises one or more heterologous nucleotidesequences encoding three enzymes of the MEV pathway. In someembodiments, the myrcene producing microbial host cell comprises one ormore heterologous nucleotide sequences encoding four enzymes of the MEVpathway. In some embodiments, the myrcene producing microbial host cellcomprises one or more heterologous nucleotide sequences encoding fiveenzymes of the MEV pathway. In some embodiments, the myrcene producingmicrobial host cell comprises one or more heterologous nucleotidesequences encoding six enzymes of the MEV pathway. In some embodiments,the myrcene producing microbial host cell further comprises aheterologous nucleotide sequence encoding an enzyme that can convert IPPgenerated via the mevalonate pathway into its isomer, dimethylallylpyrophosphate (“DMAPP”). IPP and DMAPP can be condensed and modifiedthrough the action of geranyl pyrophosphate synthase and myrcenesynthase to produce myrcene (FIG. 1 and FIG. 2A).

7.4.3. DXP Pathway Enzymes

In some embodiments of the methods provided herein, the myrceneproducing microbial host cell comprises one or more heterologousnucleotide sequences encoding one or more enzymes of the DXP pathway,which effects increased production of one or more myrcene as compared toa genetically unmodified parent cell. The DXP pathway shown in FIG. 2Bis an alternative biosynthetic pathway for producing intermediatemetabolites, such as DMAPP, which can be catalyzed for the formation ofGPP.

In some embodiments, the myrcene producing microbial host cell comprisesa heterologous nucleotide sequence encoding an enzyme, e.g.,1-deoxy-D-xylulose-5-phosphate synthase, which can condense pyruvatewith D-glyceraldehyde 3-phosphate to make1-deoxy-D-xylulose-5-phosphate. Illustrative examples of nucleotidesequences encoding such an enzyme include but are not limited to:(AF035440; Escherichia coli), (NC_002947, locus tag PP0527; Pseudomonasputida KT2440), (CP000026, locus tag SPA2301; Salmonella entericaParatyphi, see ATCC 9150), (NC_007493, locus tag RSP_0254; Rhodobactersphaeroides 2.4.1), (NC_005296, locus tag RPA0952; Rhodopseudomonaspalustris CGA009), (NC_004556, locus tag PD1293; Xylella fastidiosaTemecula1), and (NC_003076, locus tag AT5G11380; Arabidopsis thaliana).

In some embodiments, the myrcene producing microbial host cell comprisesa heterologous nucleotide sequence encoding an enzyme, e.g.,1-deoxy-D-xylulose-5-phosphate reductoisomerase, which can convert1-deoxy-D-xylulose-5-phosphate to 2C-methyl-D-erythritol-4-phosphate.Illustrative examples of nucleotide sequences include but are notlimited to: (AB013300; Escherichia coli), (AF148852; Arabidopsisthaliana), (NC_002947, locus tag PP1597; Pseudomonas putida KT2440),(AL939124, locus tag SCO5694; Streptomyces coelicolor A3(2)),(NC_007493, locus tag RSP_2709; Rhodobacter sphaeroides 2.4.1), and(NC_007492, locus tag Pfl_1107; Pseudomonas fluorescens PfO-1).

In some embodiments, the myrcene producing microbial host cell comprisesa heterologous nucleotide sequence encoding an enzyme, e.g.,4-diphosphocytidyl-2C-methyl-D-erythritol synthase, which can convert2C-methyl-D-erythritol-4-phosphate to4-diphosphocytidyl-2C-methyl-D-erythritol. Illustrative examples ofnucleotide sequences include but are not limited to: (AF230736;Escherichia coli), (NC_007493, locus tag RSP_2835; Rhodobactersphaeroides 2.4.1), (NC_003071, locus tag AT2G02500; Arabidopsisthaliana), and (NC_002947, locus tag PP1614; Pseudomonas putida KT2440).

In some embodiments, the myrcene producing microbial host cell comprisesa heterologous nucleotide sequence encoding an enzyme, e.g.,4-diphosphocytidyl-2C-methyl-D-erythritol kinase, which can convert4-diphosphocytidyl-2C-methyl-D-erythritol to4-diphosphocytidyl-2C-methyl-D-erythritol-2-phosphate. Illustrativeexamples of nucleotide sequences include but are not limited to:(AF216300; Escherichia coli) and (NC_007493, locus tag RSP_1779;Rhodobacter sphaeroides 2.4.1).

In some embodiments, the myrcene producing microbial host cell comprisesa heterologous nucleotide sequence encoding an enzyme,2C-methyl-D-erythritol 2,4-cyclodiphosphate synthase, which can convert4-diphosphocytidyl-2C-methyl-D-erythritol-2-phosphate to2C-methyl-D-erythritol 2,4-cyclodiphosphate. Illustrative examples ofnucleotide sequences include but are not limited to: (AF230738;Escherichia coli), (NC_007493, locus tag RSP_6071; Rhodobactersphaeroides 2.4.1), and (NC_002947, locus tag PP1618; Pseudomonas putidaKT2440).

In some embodiments, the myrcene producing microbial host cell comprisesa heterologous nucleotide sequence encoding an enzyme, e.g.,1-hydroxy-2-methyl-2-(E)-butenyl-4-diphosphate synthase, which canconvert 2C-methyl-D-erythritol 2,4-cyclodiphosphate to1-hydroxy-2-methyl-2-(E)-butenyl-4-diphosphate. Illustrative examples ofnucleotide sequences include but are not limited to: (AY033515;Escherichia coli), (NC_002947, locus tag PP0853; Pseudomonas putidaKT2440), and (NC_007493, locus tag RSP_2982; Rhodobacter sphaeroides2.4.1).

In some embodiments, the myrcene producing microbial host cell comprisesa heterologous nucleotide sequence encoding an enzyme, e.g.,isopentyl/dimethylallyl diphosphate synthase, which can convert1-hydroxy-2-methyl-2-(E)-butenyl-4-diphosphate into either IPP or itsisomer, DMAPP. Illustrative examples of nucleotide sequences include butare not limited to: (AY062212; Escherichia coli) and (NC_002947, locustag PP0606; Pseudomonas putida KT2440).

In some embodiments, the myrcene producing microbial host cell comprisesone or more heterologous nucleotide sequences encoding more than oneenzyme of the DXP pathway. In some embodiments, the myrcene producingmicrobial host cell comprises one or more heterologous nucleotidesequences encoding two enzymes of the DXP pathway. In some embodiments,the myrcene producing microbial host cell comprises one or moreheterologous nucleotide sequences encoding three enzymes of the DXPpathway. In some embodiments, the myrcene producing microbial host cellcomprises one or more heterologous nucleotide sequences encoding fourenzymes of the DXP pathway. In some embodiments, the myrcene producingmicrobial host cell comprises one or more heterologous nucleotidesequences encoding five enzymes of the DXP pathway. In some embodiments,the myrcene producing microbial host cell comprises one or moreheterologous nucleotide sequences encoding six enzymes of the DXPpathway. In some embodiments, the myrcene producing microbial host cellcomprises one or more heterologous nucleotide sequences encoding sevenenzymes of the DXP pathway.

In some embodiments, the myrcene producing cell further comprises aheterologous nucleotide sequence encoding an enzyme that can convert IPPgenerated via the MEV pathway into DMAPP, e.g., an IPP isomerase.Illustrative examples of nucleotide sequences encoding such an enzymeinclude, but are not limited to: (NC_000913, 3031087.3031635;Escherichia coli), and (AF082326; Haematococcus pluvialis).

In some embodiments, “cross talk” (or interference) between themicrobial host cell's own metabolic processes and those processesinvolved with the production of IPP are minimized or eliminatedentirely. For example, cross talk is minimized or eliminated entirelywhen the host microorganism relies exclusively on the DXP pathway forsynthesizing IPP, and a MEV pathway is introduced to provide additionalIPP. Such a host organism would not be equipped to alter the expressionof the MEV pathway enzymes or process the intermediates associated withthe MEV pathway. Organisms that rely exclusively or predominately on theDXP pathway include, for example, Escherichia coli.

In some embodiments, the microbial host cell produces IPP via the MEVpathway, either exclusively or in combination with the DXP pathway. Inother embodiments, a host's DXP pathway is functionally disabled so thatthe host cell produces IPP exclusively through a heterologouslyintroduced MEV pathway. The DXP pathway can be functionally disabled bydisabling gene expression or inactivating the function of one or more ofthe DXP pathway enzymes.

7.4.4. Modification of Other Enzymes for Biosynthesis of Myrcene andIdentification of Other Useful Homologous Enzymes

Described above are examples of specific biosynthetic enzymes and genesuseful in the methods and compositions according to certain embodiments;however, it will be recognized that absolute identity to such enzymesand genes are not necessary. For example, the sequences of knownbiosynthetic pathway enzymes may be modified by substitutions,insertions, and deletions. In some embodiments, such changes compriseconservative amino acid mutations and silent mutations. In otherembodiments, the nucleotide sequences encoding other biosyntheticpathway enzymes may be modified to reflect the codon preferences for aparticular host cell as described above in relation to myrcene synthasesequences. The use of preferred codons for a particular host cellgenerally increases the likelihood of translation, and hence expression,of the nucleotide sequence. Furthermore, any of the genes encoding theforegoing enzymes (or any others mentioned herein or any of theregulatory elements that control or modulate expression thereof) may beoptimized by genetic/protein engineering techniques, such as directedevolution and/or rational mutagenesis. For example, the activity of anenzyme in a host can be altered in a number of ways, including, but notlimited to, expressing a modified form of the enzyme that has a higheror lower Kea or a lower or higher K_(m) for the substrate, or expressingan altered form of the enzyme that is more or less affected by feedbackor feed-forward regulation by another molecule in the pathway. Thechanges in a particular gene or polynucleotide comprising a sequenceencoding an enzyme can be performed, and screened for expression oractivity of functional enzymes using known methods in the art.

In addition, genes encoding these enzymes can be identified from otherfungal, bacterial, plant or other species, and can be expressed for themodulation of this biosynthetic pathway. A variety of organisms couldserve as sources for these enzymes, including, but not limited to,Saccharomyces spp., including S. cerevisiae and S. uvarum, Kluyveromycesspp., including K. thermotolerans, K. lactis, and K. marxianus, Pichiaspp., Hansenula spp., including H. polymorpha, Candida spp.,Trichosporon spp., Yamadazyma spp., including Y. spp. stipitis,Torulaspora pretoriensis, Issatchenkia orientalis, SchizoSaccharomycesspp., including S. pombe. Cryptococcus spp., Aspergillus spp.,Neurospora spp., or Ustilago spp. Sources of genes from anaerobic fungiinclude, but are not limited to, Piromyces spp., Orpinomyces spp., orNeocallimastix spp. Sources of prokaryotic enzymes that are usefulinclude, but are not limited to, Escherichia coli, Zymomonas mobilis,Staphylococcus aureus, Bacillus spp., Clostridium spp., Corynebacteriumspp., Pseudomonas spp., Lactococcus spp., Enterobacter spp., andSalmonella spp. In certain embodiments, sequences encoding biosyntheticpathway enzymes may be obtained from plant species. These include, butare not limited to, Picea abies, Glycine max, Medicago sativa,Phalaenopsis bellina, Salvia miltiorrhiza, and Mangifera indica.

Techniques known to those skilled in the art may be suitable to identifyadditional homologous genes and homologous enzymes. Generally,homologous genes and/or homologous enzymes can be identified byfunctional analysis and will have functional similarities. Techniquesknown to those skilled in the art may be suitable to identify analogousgenes enzymes. For example, to identify homologous GGPS genes, proteins,or enzymes, techniques may include, but are not limited to, cloning agene by PCR using primers based on a published sequence of a GPPSgene/enzyme or by degenerate PCR using degenerate primers designed toamplify a conserved region among GPPS genes. Further, one skilled in theart can use techniques to identify homologous genes, proteins, orenzymes with functional homology or similarity. Techniques includeexamining a cell or cell culture for the catalytic activity of an enzymethrough in vitro enzyme assays for said activity (e.g. as describedherein or in Kiritani, K., Branched-Chain Amino Acids MethodsEnzymology, 1970), then isolating the enzyme with said activity throughpurification. The protein sequence of the enzyme can be determinedthrough techniques such as Edman degradation; PCR primers to the likelynucleic acid sequence can be designed; the DNA sequence can be amplifiedthrough PCR; and the nucleic acid sequence can be cloned. To identifyhomologous or similar genes and/or homologous or similar enzymes,techniques also include comparison of data concerning a candidate geneor enzyme with databases such as BRENDA, KEGG, or MetaCYC. The candidategene or enzyme may be identified within the above mentioned databases.

7.5 Preparation of Nucleic Acid Molecules, Constructs and ExpressionVectors

Preparation of the nucleic acid molecules described herein can becarried out by a variety of routine recombinant techniques and syntheticprocedures. Briefly, the nucleic acid molecules can be prepared fromgenomic DNA fragments, cDNAs, and RNAs, all of which can be extracteddirectly from a cell or can be recombinantly produced by variousamplification processes including, but not limited to, PCR and rt-PCR.These and other recombinant techniques are described in, e.g., Sambrooket al., 2001, Molecular Cloning—A Laboratory Manual, 3rd edition, ColdSpring Harbor Laboratories, Cold Spring Harbor, N.Y., and Ausubel etal., eds. Current Edition, Current Protocols in Molecular Biology,Greene Publishing Associates and Wiley Interscience, N.Y.

Direct chemical synthesis of nucleic acid molecules typically involvessequential addition of 3′-blocked and 5′-blocked nucleotide monomers tothe terminal 5′-hydroxyl group of a growing nucleotide polymer chain,wherein each addition is effected by nucleophilic attack of the terminal5′-hydroxyl group of the growing chain on the 3′-position of the addedmonomer, which is typically a phosphorus derivative, such as aphosphotriester, phosphoramidite, or the like. Such methodology is knownto those of ordinary skill in the art and is described in the pertinenttexts and literature (for example, Matteuci et al. (1980) Tet. Lett.521:719; U.S. Pat. No. 4,500,707 to Caruthers et al.; and U.S. Pat. Nos.5,436,327 and 5,700,637 to Southern et al.).

In addition, the nucleic acid molecules can be custom ordered throughvarious commercial sources. These include, for example, Twist Bioscience(San Francisco, Calif.), Biomatik (Wilmington, Del.), Genescript(Piscataway, N.J.), and GeneArt gene synthesis services availablethrough www.introgen.com.

In addition, provided herein are nucleic acid constructs comprising anisolated nucleic acid molecule operably linked to one or more controlsequences that direct the expression of the coding sequence in asuitable microbial host cell under conditions compatible with thecontrol sequences. The control sequence may include any suitablepromoter sequence, transcription terminal sequence, a polyadenylationsequence, and the like. In certain embodiments, these control sequencesmay be any nucleotide sequences that regulate transcriptional activityin the microbial host cell of choice and may be obtained from genesencoding one or more enzymes in the biosynthetic pathway homologous orheterologous to the microbial host cell.

Various control sequences for expression in microbial host cells arewell-known in the art. For example, useful promoters for expression inyeast host cells can be derived from genes homologous to the transformedmicrobial host cell and/or native to the production host. In someembodiments, promoters operably linked to the nucleic acid molecule areinducible. In other embodiments, the promoters operably linked to thenucleic acid molecule encoding a coding sequence are constitutive. Insome embodiments, one or more nucleic acid sequences are operably linkedto an inducible promoter, and one or more other nucleic acid sequencesare operably linked to a constitutive promoter. Illustrative examples ofpromoters suitable for use in yeast cells include, but are not limitedto the promoter of the TEF1 gene of K. lactis, the promoter of the PGK1gene of Saccharomyces cerevisiae, the promoter of the TDH3 gene ofSaccharomyces cerevisiae, repressible promoters, e.g., the promoter ofthe CTR3 gene of Saccharomyces cerevisiae, and inducible promoters,e.g., galactose inducible promoters of Saccharomyces cerevisiae (e.g.,promoters of the GAL1, GAL2, GAL7, and GAL10 genes). Additionalpromoters and other control sequences for microbial host cells aredescribed by, e.g., Romanos et al., 1992, Yeast 8: 423-488; Bitter etal., 1987, Methods in Enzymology, 153:516-544; and Maximizing GeneExpression, ed. Reznikoff and Gold, 2014, Elsevier.

Also provided herein are vectors comprising nucleic acid constructscomprising nucleic acid molecules encoding biosynthetic pathway enzymesincluding the myrcene synthases that catalyze the formation of myrceneand other monoterpenes. Vectors useful for the transformation ofsuitable microbial host cells are well-known in the art. In someembodiments, the vector contains control sequences directingtranscription and translation of the relevant gene, a selectable marker,and sequences allowing autonomous replication or chromosomalintegration. Suitable vectors comprise a region 5′ of the codingsequence which harbors transcriptional initial controls and a region 3′of the coding sequence which controls transcriptional termination.

The vectors may be any vector that is suitable for expressing theenzymes. Expression vectors useful for expressing polypeptide-encodingnucleotide sequences include viral vectors (e.g., retroviruses,adenoviruses and adeno-associated viruses), plasmid vectors, andcosmids. Illustrative examples of expression vectors suitable for use inyeast cells include, but are not limited to CEN/ARS and 2p plasmids. Thechoice of vector will depend on the compatibility of the vector with themicrobial host cells into which the vector to be introduced and the endapplication of the host cell. In some embodiments, the vector may be achromosomal integration construct which further include element(s) thatpermits integration of the vector into the host cell's genome. In otherembodiments, the vectors may be expression vectors that are autonomouslyreplicating and exist extrachromosomally in host cells. Suitable vectorsfor microbial host cells are described in, e.g., “Cloning Vectors forIntroducing Genes into Host cells,” The ABCs of Gene Cloning, 2006, pp.93-124, Springer US. Protein Expression, a Practical Approach, Higginsand Hames, Oxford University Press 1999. Vectors suitable for microbialhost cells are also commercially available from various sources, e.g.,Life Technologies, Sigma-Aldrich, New England BioLabs, and the like.

The procedures used to ligate the elements described above to constructthe recombinant expression vectors or chromosomally integratingconstructs are well known to those skilled in the art (see, e.g.,Sambrook et al., 1989, supra).

7.6 Genetically Modified Microbial Host Cells

Provided herein are genetically modified microbial host cells thatproduce heterologous myrcene. The heterologous nucleic acid moleculesencoding myrcene synthases, geranyl pyrophosphate synthases, and/orother biosynthetic pathway enzymes may be introduced into the microbialhost cells using any suitable vectors described herein and known in theart. Methods for genetically modifying microbes using expression vectorsor chromosomal constructs in a host cell are well known in the art. See,e.g., Sherman, F., et al., Methods Yeast Genetics, Cold Spring HarborLaboratory, N.Y. (1978); Guthrie, C., et al. (Eds.) Guide To YeastGenetics and Molecular Biology Vol. 194, Academic Press, San Diego(1991); Sambrook et al., 2001, Molecular Cloning—A Laboratory Manual,3^(rd) edition, Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y.;and Ausubel et al., eds., Current Edition, Current Protocols inMolecular Biology, Greene Publishing Associates and Wiley Interscience,NY.; the disclosures of which are incorporated herein by reference.

Exemplary techniques for host cell transformation include, but are notlimited to, spheroplasting, electroporation, PEG 1000 mediatetransformation, and lithium acetate or lithium chloride mediatedtransformation. Furthermore, heterologous nucleic acid molecules may beintegrated into the selected site in the host genome via any suitabletechniques. For example, specific genome sites may be targeted by sitespecific nucleases (e.g., Zinc Finger Nucleases, Meganucleases,Transcription Activator-Like Effector Nucleases, CRISPR/Cas system) toinduce targeted mutagenesis, induce targeted deletions of cellular DNAsequences, and facilitate targeted recombination of heterologous nucleicacid molecules within the targeted genomic site. See, e.g., U.S. Pat.No. 8,685,737; and Horwitz et al. (2015), Cell Systems 1, 1-9, U.S.Patent Publication No. 20030232410; 20050208489; 20050026157;20050064474; and 20060188987, and WO 2007/014275, the disclosures ofwhich are incorporated herein by reference in their entirety for allpurposes.

In certain embodiments, the microbial host cells can further comprisegenetic modifications (e.g., insertions, deletions, or modifications ofnucleic acids) in such a manner as to provide the desired effect ofelevating the intracellular level of geranyl pyrophosphate, ofexpressing the myrcene synthases described herein, or of production ofmyrcene. For example, the endogenous farnesyl pyrophosphate synthase inthe host genome may be functionally disrupted to increase carbon flowtowards production of geranyl pyrophosphate precursor and myrcene.

Furthermore, the copy number of one or more biosynthetic enzymes in ahost cell may be altered by modifying the transcription of the gene thatencodes the enzyme. This can be achieved for example by modifying thecopy number of the nucleotide sequence encoding the enzyme, for example,by using a higher or lower copy number expression vector comprising thenucleotide sequence, or by introducing additional copies of thenucleotide sequence into the genome of the host cell. For example, 2, 3,4, 5, 6, 7, 8, 9, 10 or more copies of a myrcene synthase gene may bechromosomally integrated into the genome of microbial host cells. Inanother example, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more copies of a geranylpyrophosphate synthase gene may be chromosomally integrated into thegenome of microbial host cells. In certain embodiments, the copy numberof a myrcene synthase gene and the copy number of a geranylpyrophosphate synthase gene may be adjusted relative to each other toincrease carbon flow toward production of myrcene. In some embodiments,the copy number of a myrcene synthase gene integrated into the genome ofa microbial host cell is equal to or greater than the copy number of ageranyl pyrophosphate gene integrated into the genome of the microbialhost cell.

In addition, inhibition of gene expression or decreased expressionlevel, which results in increased production of myrcene in host cells,may be accomplished by deleting or disrupting the nucleotide sequence inthe genome of the host cell, mutation, and/or gene rearrangement. It canalso be carried out with the use of antisense RNA, siRNA, miRNA,ribozymes, triple stranded DNA, a trans-acting DNA binding protein suchas TAL effector or CRISPR guided Cas9, and transcription and/ortranslation inhibitors. In addition, transposons can be employed todisrupt gene expression, for example, by inserting it between thepromoter and the coding region, or between two adjacent genes toinactivate one or both genes. The additional modification may includechanging the order of coding sequences on a polycistronic mRNA of anoperon or breaking up an operon into individual genes each with its owncontrol elements, or by increasing the strength of the promoter oroperator to which the nucleotide sequence is operably linked. In someversions, a gene or coding sequence can be replaced with a selectionmarker or screenable marker. Various methods for introducing the geneticmodifications described above are well known in the art and includehomologous recombination, among other mechanisms. See, e.g., Green etal., Molecular Cloning: A laboratory manual, 4th ed., Cold Spring HarborLaboratory Press (2012) and Sambrook et al., Molecular Cloning: ALaboratory Manual, 3rd ed., Cold Spring Harbor Laboratory Press (2001).

Alternatively or additionally, the copy number of an enzyme in a hostcell may be altered by modifying the level of translation of an mRNAthat encodes the enzyme. This can be achieved, for example, by modifyingthe stability of the mRNA, modifying the sequence of the ribosomebinding site, modifying the distance or sequence between the ribosomebinding site and the start codon of the enzyme coding sequence,modifying the entire intercistronic region located upstream of oradjacent to the 5′ side of the start codon of the enzyme coding region,stabilizing the 3′-end of the mRNA transcript using hairpins andspecialized sequences, and the like.

Genetic modifications of microbial host cells are not limited to thespecific modifications described herein. Other suitable means forgenetically modifying microbial host cells apparent to those skilled inthe art are also within the scope of the present invention and can beemployed to increase carbon flow through the biosynthetic pathway toincrease production of myrcene.

7.6.1. Microbial Host Cells

Microbial host cells useful in the methods and compositions providedherein include any cell capable of naturally or recombinantly producingmyrcene. In some embodiments, the cell is a prokaryotic cell. In someembodiments, the cell is a bacterial cell. In some embodiments, the cellis an Escherichia coli cell. In some embodiments, the cell is aeukaryotic cell. In some embodiments, the cell is a unicellulareukaryotic organism cell. In some embodiments, the cell is a yeast cell.In some embodiments, the cell is a Saccharomyces cerevisiae cell.

In some embodiments, the microbial host cell is a mycelial bacterialcell. In some embodiments, the mycelial bacterial cell is of the classactinomycetes. In particular embodiments, the mycelial bacterial cell isof the genera Streptomyces, for example, Streptomyces ambofaciens,Streptomyces avermitilis, Streptomyces azureus, Streptomycescinnamonensis, Streptomyces coelicolor, Streptomyces curacoi,Streptomyces erythraeus, Streptomyces fradiae, Streptomyces galilaeus,Streptomyces glaucescens, Streptomyces hygroscopicus, Streptomyceslividans, Streptomyces parvulus, Streptomyces peucetius, Streptomycesrimosus, Streptomyces roseofulvus, Streptomyces thermotolerans, andStreptomyces violaceoruber.

In another embodiment, the microbial host cell is a fungal cell. In amore particular embodiment, the cell is a yeast cell. Yeasts useful inthe methods and compositions provided herein include yeasts that havebeen deposited with microorganism depositories (e.g. IFO, ATCC, etc.)and belong to the genera Aciculoconidium, Ambrosiozyma, Arthroascus,Arxiozyna, Ashbya, Babjevia, Bensingtonia, Botryoascus, Botryozyma,Brettanomyces, Bullera, Bulleromyces, Candida, Citeromyces, Clavispora,Cryptococcus, Cystofilobasidium, Debaryomyces, Dekkara, Dipodascopsis,Dipodascus, Eeniella, Endomycopsella, Eremascus, Eremothecium,Erythrobasidium, Fellomyces, Filobasidium, Galactomyces, Geotrichum,Guilliermondella, Hanseniaspora, Hansenula, Hasegawaea, Holtermannia,Hormoascus, Hyphopichia, Issatchenkia, Kloeckera, Kloeckeraspora,Kluyveromyces, Kondoa, Kuraishia, Kurtzmanomyces, Leucosporidium,Lipomyces, Lodderomyces, Malassezia, Metschnikowia, Mrakia, Myxozyma,Nadsonia, Nakazawaea, Nematospora, Ogataea, Oosporidium, Pachysolen,Phachytichospora, Phaffia, Pichia, Rhodosporidium, Rhodotorula,Saccharomyces, Saccharomycodes, Saccharomycopsis, Saitoella, Sakaguchia,Saturnospora, Schizoblastosporion, SchizoSaccharomyces, Schwanniomyces,Sporidiobolus, Sporobolomyces, Sporopachydermia, Stephanoascus,Sterigmatomyces, Sterigmatosporidium, Symbiotaphrina, Sympodiomyces,Sympodiomycopsis, Torulaspora, Trichosporiella, Trichosporon,Trigonopsis, Tsuchiyaea, Udeniomyces, Waltomyces, Wickerhamia,Wickerhamiella, Williopsis, Yamadazyma, Yarrowia, Zygoascus,ZygoSaccharomyces, Zygowilliopsis, and Zygozyma, among others.

In particular embodiments, useful yeasts in the methods and compositionsprovided herein include Saccharomyces cerevisiae, Pichia pastoris,SchizoSaccharomyces pombe, Dekkera bruxellensis, Kluyveromyces lactis(previously called Saccharomyces lactis), Kluveromyces marxianus, Arxulaadeninivorans, or Hansenula polymorpha (now known as Pichia angusta). Insome embodiments, the microbe is a strain of the genus Candida, such asCandida lipolytica, Candida guilliermondii, Candida krusei, Candidapseudotropicalis, or Candida utilis.

In a particular embodiment, the cell is a Saccharomyces cerevisiae cell.In some embodiments, the strain of the Saccharomyces cerevisiae cell isselected from the group consisting of Baker's yeast, CBS 7959, CBS 7960,CBS 7961, CBS 7962, CBS 7963, CBS 7964, IZ-1904, TA, BG-1, CR-1, SA-1,M-26, Y-904, PE-2, PE-5, VR-1, BR-1, BR-2, ME-2, VR-2, MA-3, MA-4,CAT-1, CB-1, NR-1, BT-1, and AL-1. In some embodiments, the strain ofSaccharomyces cerevisiae is selected from the group consisting of PE-2,CAT-1, VR-1, BG-1, CR-1, and SA-1. In a particular embodiment, thestrain of Saccharomyces cerevisiae is PE-2. In another particularembodiment, the strain of Saccharomyces cerevisiae is CAT-1. In anotherparticular embodiment, the strain of Saccharomyces cerevisiae is BG-1.

In some embodiments, the cell is a haploid microbial cell. In otherembodiments, the cell is a diploid microbial cell. In some embodiments,the cell is heterozygous. In other embodiments, the cell is homozygousother than for its mating type allele (i.e., if the cell shouldsporulate, the resulting four haploid microbial cells would begenetically identical except for their mating type allele, which in twoof the haploid cells would be mating type a and in the other two haploidcells would be mating type alpha).

In some embodiments, the cell is suitable for industrial fermentation.In particular embodiments, the cell is conditioned to subsist under highsolvent concentration, high temperature, expanded substrate utilization,nutrient limitation, oxygen limitation, osmotic stress, acidity, sulfiteand bacterial contamination, or combinations thereof, which arerecognized stress conditions of the industrial fermentation environment.In particular embodiments, the cell is conditioned to subsist under highmycene concentration.

7.7 Fermentation Compositions and Production of Myrcene

In another aspect, provided herein are fermentation compositionsproduced by genetically modified microbial host cells and methods forproducing myrcene. The fermentation is performed by culturing thegenetically modified microbial host cells in a culture medium comprisinga carbon source under suitable culture conditions for a period of timesufficient to produce a desired biomass of host cells and/or a desiredamount of myrcene.

In certain embodiments, the fermentation process is carried out in twostages—a build stage and a production stage. The build stage is carriedout for a period of time sufficient to produce an amount of cellularbiomass that can support production of myrcene during the productionstage. The build stage is carried out for a period of time sufficientfor the population present at the time of inoculation to undergo aplurality of doublings until a desired cell density is reached. In someembodiments, the build stage is carried out for a period of timesufficient for the host cell population to reach a cell density (OD₆₀₀)of between 0.01 and 400 in the fermentation vessel or container in whichthe build stage is being carried out. In some embodiments, the buildstage is carried out until an OD₆₀₀ of at least 0.01 is reached. In someembodiments, the build stage is carried out until an OD₆₀₀ of at least0.1 is reached. In some embodiments, the build stage is carried outuntil an OD₆₀₀ of at least 1.0 is reached. In some embodiments, thebuild stage is carried out until an OD₆₀₀ of at least 10 is reached. Insome embodiments, the build stage is carried out until an OD₆₀₀ of atleast 100 is reached. In some embodiments, the build stage is carriedout until an OD₆₀₀ of between 0.01 and 100 is reached. In someembodiments, the build stage is carried out until an OD₆₀₀ of between0.1 and 10 is reached. In some embodiments, the build stage is carriedout until an OD₆₀₀ of between 1 and 100 is reached. In otherembodiments, the build stage is carried for a period of at least 12, 24,36, 48, 60, 72, 84, 96 or more than 96 hours.

In some embodiments, the production stage is carried out for a period oftime sufficient to produce a desired amount of myrcene. In someembodiments, the production stage is carried out for a period of atleast 12, 24, 36, 48, 60, 72, 84, 96 or more than 96 hours. In someembodiments, the production stage is carried out for a period of between3 and 20 days. In some embodiments, the production stage is carried fora period of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17,18, 19, 20 or more than 20 days.

In a particular embodiment, the method of producing myrcene comprisesconducting fermentation of the genetically modified host cell underaerobic conditions sufficient to allow growth and maintenance of thegenetically modified host cell; then subsequently providing microaerobicfermentation conditions sufficient to induce production of myrcene (andother monoterpene co-products), and maintaining the microaerobicconditions throughout the fermentation run. In certain embodiments, themicroaerobic conditions are used throughout the fermentation run. Incertain embodiments, an inducing agent is added during the productionstage to activate a promoter or to relieve repression of atranscriptional regulator to promote production of myrcene and othermonoterpene co-products.

In another embodiment, the method of producing myrcene comprisesculturing the microbial host cells in separate build and productionculture media. For example, the method can comprise culturing thegenetically modified microbial host cell in a build stage wherein thecell is cultured under non-producing conditions (e.g., non-inducingconditions) to produce an inoculum, then transferring the inoculum intoa second fermentation medium under conditions suitable to induce myrceneproduction (e.g., inducing conditions), and maintaining steady stateconditions in the second fermentation stage to produce a cell culturecontaining myrcene.

7.7.1. Culture Media and Conditions

Culture media and culture conditions for the maintenance and growth ofmicrobial cultures are well known to those skilled in the art ofmicrobiology or fermentation science (see, for example, Bailey et al.,Biochemical Engineering Fundamentals, second edition, McGraw Hill, NewYork, 1986). Appropriate culture medium, pH, temperature, andrequirements for aerobic, microaerobic, or anaerobic conditions may beselected depending on the specific requirements of the microbial hostcell, the fermentation, and the process.

In some embodiments, the culture medium for use in the methods ofproducing myrcene as provided herein includes any culture medium inwhich a genetically modified microorganism capable of producingmonoterpenes can subsist, i.e., support and maintain growth andviability. In some embodiments, the culture medium, also promotes thebiosynthetic pathway necessary to produce the desired monoterpenes, inparticular myrcene.

In some embodiments, the culture medium is an aqueous medium comprisingassimilable carbon, nitrogen and phosphate sources. Such a medium canalso include appropriate salts, minerals, metals and other nutrients. Insome embodiments, the carbon source and each of the essential cellnutrients are added incrementally or continuously to the fermentationmedia, and each required nutrient is maintained at essentially theminimum level needed for efficient assimilation by growing cells, forexample, in accordance with a predetermined cell growth curve based onthe metabolic or respiratory function of the cells which convert thecarbon source to a biomass.

In some embodiments, the carbon source is a monosaccharide (simplesugar), a disaccharide, a polysaccharide, a non-fermentable carbonsource, or one or more combinations thereof. Non-limiting examples ofsuitable monosaccharides include glucose, galactose, mannose, fructose,ribose, and combinations thereof. Non-limiting examples of suitabledisaccharides include sucrose, lactose, maltose, trehalose, cellobiose,and combinations thereof. Non-limiting examples of suitablepolysaccharides include starch, glycogen, cellulose, chitin, andcombinations thereof. Non-limiting examples of suitable non-fermentablecarbon sources include acetate and glycerol. In some embodiments, thecarbon source may be derived from a wide variety of crops and sources.Some non-limiting examples of suitable crops or sources include sugarcane, bagasse, miscanthus, sugar beet, sorghum, grain sorghum,switchgrass, barley, hemp, kenaf, potatoes, sweet potatoes, cassava,sunflower, fruit, molasses, whey or skim milk, corn, stover, grain,wheat, wood, paper, straw, cotton, many types of cellulose waste, andother biomass. In certain embodiments, the suitable crops or sourcesinclude sugar cane, sugar beet and corn. In other embodiments, the sugarsource is cane juice or molasses. In certain embodiments, anycombination of the above carbon sources may be used.

In some embodiments, the suitable medium is supplemented with one ormore additional agents, such as, for example, an inducer (e.g., when oneor more nucleotide sequences encoding a gene product are under thecontrol of an inducible promoter), a repressor (e.g., when one or morenucleotide sequences encoding a gene product are under the control of arepressible promoter), or a selection agent (e.g., an antibiotic toselect for microorganisms comprising the genetic modifications).

In certain embodiments, a liquid organic overlay may be added to theculture medium during the production stage of the fermentation. Incertain embodiments, a liquid organic overlay is an immiscible organicliquid which is in contact with the aqueous culture medium, and myrceneand other co-products secreted from microorganisms can be captured inthe liquid organic overlay. A liquid organic overlay can reduceevaporation of volatile monoterpenes from the fermentation vessel aswell reduce potential myrcene toxicity to microorganisms. Examples of anoverlay include, but are not limited to, isopropyl myristate (IPM) orother hydrocarbon liquids such as white mineral oils orpolyalphaolefins.

The fermentation methods may be performed in a suitable container orvessel, including but not limited to, a cell culture plate, a flask, ora fermentor. In certain embodiments, the fermentation is conducted in aclosed system to trap monoterpenes in the gas phase. For example, theclosed system may include a series of vessels connected to one anotherto trap offgas including monoterpenes in the vapor phase. For example, afirst vessel may contain a culture medium comprising an aqueous mediumand genetically modified microorganisms. A second vessel comprising anorganic overlay may be connected in series with the first vessel to trapthe volatile monoterpenes. In certain embodiments, one or moreadditional vessels may be connected to the first vessel in series and/orparallel to capture a gaseous composition comprising myrcene and othermonoterpene co-products.

Furthermore, the methods can be performed at any scale of fermentationknown in the art to support industrial production of microbial products.Any suitable fermentor may be used including a stirred tank fermentor,an airlift fermentor, a bubble fermentor, or any combination thereof. Inparticular embodiments utilizing Saccharomyces cerevisiae as the hostcell, strains can be grown in a fermentor as described in detail byKosaric, et al., in Ullmann's Encyclopedia of Industrial Chemistry,Sixth Edition, Volume 12, pages 398-473, Wiley-VCH Verlag GmbH & Co.KDaA, Weinheim, Germany. Further, the methods can be performed at anyvolume of fermentation, e.g., from lab scale (e.g., 10 ml to 20 L) topilot scale (e.g., 20 L to 500 L) to industrial scale (e.g., 500 L to≥500,000 L) fermentations.

Additional details related to culture conditions and fermentationmethods suitable for certain embodiments can be found in U.S. Pat. Nos.8,603,800, 7,659,097 and WO2007/139924, which are incorporated herein byreference in their entirety for all purposes.

7.7.2. Fermentation Compositions

In another aspect, provided herein are fermentation compositionscomprising a genetically modified microbial host cell described herein,a culture medium, and monoterpenes produced from the geneticallymodified microbial host cell. In the fermentation compositions providedherein, the monoterpenes comprise myrcene as a major component and oneor more co-products (which are concurrently produced with myrcene) asminor components. In certain embodiments, the monoterpenes infermentation compositions comprise at least about 85% myrcene and lessthan about 15% monoterpene co-products (excluding geraniol), compared tothe total amount of monoterpenes, based on relative area % ofmonoterpene peaks shown in a GC chromatogram of the monoterpenes. Incertain embodiments, the fermentation composition comprises at leastabout 88% to about 93% myrcene, compared to the total amount ofmonoterpene products in the culture medium.

In certain embodiments, the fermentation compositions comprise a numberof different co-products catalyzed by the myrcene synthase in vivo ingenetically modified microbial host cells. For example, the fermentationcomposition can comprise 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 monoterpeneco-products as minor components. In certain embodiments, thefermentation compositions comprise 4-terpineol as one of monoterpenesco-products concurrently produced with myrcene as shown in FIG. 3B. Bycontrast, other myrcene synthases, such as those obtained from Quercusilex (QiMS), do not produce 4-terpineol. See, e.g., FIG. 3A. In certainembodiments, the present fermentation compositions further compriseγ-terpinene and α-terpinene, which are not produced by other myrcenesynthases. See, e.g., FIG. 3A. In other embodiments, the minorco-products may further comprise sabinene, limonene, β-ocimene, and/orβ-linalool. In yet other embodiments, the minor co-products may furthercomprise α-thujene, (E)-sabinene hydrate, and/or (Z)-sabinene hydrate.In particular embodiment, the fermentation composition comprises myrceneas a major component, and γ-terpinene, α-terpinene, sabinene, limonene,β-ocimene, β-linalool, and/or 4-terpineol as minor components. Inparticular embodiment, the fermentation comprises myrcene as a majorcomponent, and γ-terpinene, α-terpinene, sabinene, limonene, β-ocimene,β-linalool, α-thujene, (E)-sabinene hydrate, and (Z)-sabinene hydrate,and/or 4-terpineol as minor components.

In certain embodiments, each of monoterpene co-products is concurrentlyproduced with myrcene at a level detectable by GC-FID or GC-MS but in asmall amount relative to myrcene. In certain embodiments, eachmonoterpene co-product is present in the fermentation composition in anamount greater than 0.1% but less than about 5%, compared to the totalamount of monoterpenes, based on relative area % of the monoterpenes ina GC-MS. In certain embodiments, a monoterpene co-product is present inthe fermentation composition in an amount greater than 0.5% but lessthan 4%, compared to the total amount of monoterpenes, based on relativearea % of the monoterpenes in the GC-MS chromatogram. In certainembodiments, a monoterpene co-product is present in the fermentationcomposition in an amount greater than 1% but less than 3%, compared tothe total amount of monoterpenes, based on relative area % of themonoterpenes in the GC-MS chromatogram.

In particular embodiments, the fermentation composition comprises about89.09% to about 92.01% myrcene, compared to the total amount of themonoterpenes, based on relative area % of the monoterpenes in the GC-MSchromatogram. In particular embodiments, the fermentation compositionfurther comprises at least about 0.65% to 0.90% α-terpinene, compared tothe total amount of the monoterpenes, based on relative area % of themonoterpenes in the GC-MS chromatogram. In particular embodiments, thefermentation composition further comprises at least about 1.00% to about1.06% γ-terpinene, compared to the total amount of the monoterpenes,based on relative area % of the monoterpenes in the GC-MS chromatogram.In particular embodiments, the fermentation composition furthercomprises at least about 2.32% to about 2.42% 4-terpineol, compared tothe total amount of monoterpenes, based on relative area % of themonoterpenes in the GC-MS chromatogram. In particular embodiments, thefermentation composition further comprises at least about 0.80% to about0.98% sabinene, compared to the total amount of monoterpenes. Inparticular embodiments, the fermentation composition further comprisesat least about 0.54% to about 1.01% limonene, compared to the totalamount of the monoterpenes, based on relative area % of the monoterpenesin the GC-MS chromatogram. In particular embodiments, the fermentationcomposition further comprises about 0.91% to about 0.21% 0-ocimene,compared to the total amount of the monoterpenes, based on relative area% of the monoterpenes in the GC-MS chromatogram. In particularembodiments, the fermentation composition further comprises about 0.76%to about 1.17% f-linalool. In particular embodiments, the fermentationcomposition further comprises about 0% to about 0.51% α-thujene,compared to the total amount of the monoterpenes, based on relative area% of the monoterpenes in the GC-MS chromatogram. In particularembodiments, the fermentation composition further comprises about 0.54%to about 1% (E)-sabinene hydrate, compared to the total amount of themonoterpenes, based on relative area % of the monoterpenes in the GC-MSchromatogram. In certain embodiments, the fermentation compositionfurther comprises about 0.98% to about 1.13% (Z)-sabinene hydrate, basedon relative area % of the monoterpenes in the GC-MS chromatogram.

A number of myrcene synthase variants derived from Ocimum basilicumexhibit a substantially similar monoterpene product profile as thewild-type myrcene synthase of Ocimum basilicum and retain the highmyrcene production level. The Ocimum basilicum myrcene synthase and itsvariants are particularly useful in certain embodiments, because theyare capable of producing myrcene in relatively high titer duringfermentation of genetically modified microbial host cells. Furthermore,as discussed above, both wild-type Ocimum basilicum and its variantsprovided herein, when expressed in genetically modified microbial hostcells, produce a unique monoterpene product profile, which isdistinguishable from monoterpene product profiles produced by myrcenesynthases derived from other organisms. For example, the presentlydescribed myrcene synthases, when expressed in genetically modifiedmicrobial host cells, produce one or more of α-terpinene and γ-terpineneas monoterpene co-products together with myrcene. By contrast, theseco-products are not produced with myrcene by other myrcene synthases,such as Quercus ilex myrcene synthase. Therefore, the monoterpenesproduced from the presently provided myrcene synthase sequences have aunique molecular fingerprint, which cannot be imparted by myrcenesynthase sequences derived from other organisms.

In some embodiments, the myrcene is produced in an amount greater thanabout 1 gram per liter of fermentation medium. In some embodiments, themyrcene is produced in an amount greater than about 5 grams per liter offermentation medium. In some embodiments, the myrcene is produced in anamount greater than about 10 grams per liter of the fermentation medium.In some such embodiments, the myrcene is produced in an amount fromabout 10 to about 200 grams or in an amount from about 10 to about 100grams per liter of the fermentation medium. In some such embodiments,the myrcene is produced in an amount more than about 15 grams, more thanabout 20 grams, more than about 25 grams, or more than about 30 gramsper liter of the fermentation medium.

In some embodiments, the myrcene is produced in an amount greater thanabout 1 milligrams per gram of dry cell weight. In some embodiments, themyrcene is produced in an amount greater than about 10 milligrams pergram of dry cell weight. In some embodiments, the myrcene is produced inan amount greater than about 50 milligrams per gram of dry cell weight.In some embodiments, the myrcene is produced in an amount greater thanabout 50 milligrams per gram of dry cell weight. In some suchembodiments, the myrcene is produced in an amount from about 50 to about1500 milligrams, more than about 100 milligrams, more than about 150milligrams, more than about 200 milligrams, more than about 250milligrams, more than about 500 milligrams, more than about 750milligrams, or more than about 1000 milligrams per gram of dry cellweight.

In some embodiments, the myrcene is produced in an amount that is atleast about 10%, at least about 15%, at least about 20%, at least about25%, at least about 30%, at least about 35%, at least about 40%, atleast about 45%, at least about 50%, at least about 60%, at least about70%, at least about 80%, at least about 90%, at least about 2-fold, atleast about 2.5-fold, at least about 5-fold, at least about 10-fold, atleast about 20-fold, at least about 30-fold, at least about 40-fold, atleast about 50-fold, at least about 75-fold, at least about 100-fold, atleast about 200-fold, at least about 300-fold, at least about 400-fold,at least about 500-fold, or at least about 1,000-fold, or more, higherthan the amount of the myrcene produced by a microbial host cell thatdoes not comprise a heterologous nucleic acid molecule encoding amyrcene synthase, on a per unit volume of cell culture basis.

In some embodiments, the myrcene is produced in an amount that is atleast about 10%, at least about 15%, at least about 20%, at least about25%, at least about 30%, at least about 35%, at least about 40%, atleast about 45%, at least about 50/a, at least about 60%, at least about70%, at least about 80%, at least about 90%, at least about 2-fold, atleast about 2.5-fold, at least about 5-fold, at least about 10-fold, atleast about 20-fold, at least about 30-fold, at least about 40-fold, atleast about 50-fold, at least about 75-fold, at least about 100-fold, atleast about 200-fold, at least about 300-fold, at least about 400-fold,at least about 500-fold, or at least about 1,000-fold, or more, higherthan the amount of the myrcene produced by a microbial host cell thatdoes not comprise a heterologous nucleic acid molecule encoding amyrcene synthase, on a per unit dry cell weight basis.

In some embodiments, the myrcene is produced in an amount that is atleast about 10%, at least about 15%, at least about 20%, at least about25%, at least about 30%, at least about 35%, at least about 40%, atleast about 45%, at least about 50%, at least about 60%, at least about70%, at least about 80%, at least about 90%, at least about 2-fold, atleast about 2.5-fold, at least about 5-fold, at least about 10-fold, atleast about 20-fold, at least about 30-fold, at least about 40-fold, atleast about 50-fold, at least about 75-fold, at least about 100-fold, atleast about 200-fold, at least about 300-fold, at least about 400-fold,at least about 500-fold, or at least about 1,000-fold, or more, higherthan the amount of the myrcene produced by a microbial host cell thatdoes not comprise a heterologous nucleic acid molecule encoding amyrcene synthase, on a per unit volume of cell culture per unit timebasis.

In some embodiments, the myrcene is produced in an amount that is atleast about 10%, at least about 15%, at least about 20%, at least about25%, at least about 30%, at least about 35%, at least about 40%, atleast about 45%, at least about 50%, at least about 60%, at least about70%, at least about 80%, at least about 90%, at least about 2-fold, atleast about 2.5-fold, at least about 5-fold, at least about 10-fold, atleast about 20-fold, at least about 30-fold, at least about 40-fold, atleast about 50-fold, at least about 75-fold, at least about 100-fold, atleast about 200-fold, at least about 300-fold, at least about 400-fold,at least about 500-fold, or at least about 1,000-fold, or more, higherthan the amount of the myrcene produced by a microbial host cell thatdoes not comprise a heterologous nucleic acid molecule encoding amyrcene synthase, on a per unit dry cell weight per unit time basis.

7.7.3. Recovery of Myrcene

The monoterpenes including myrcene produced by the genetically modifiedmicrobial host cell described herein can be isolated from thefermentation compositions using any suitable separation and purificationmethods known in the art. In certain embodiments, monoterpenes aresecreted into the culture medium and may spontaneously form a liquidorganic phase, such as an emulsion phase, separate from an aqueous phaseof the culture medium. In certain embodiments, secreted monoterpenes maypartition into an organic overlay which is added to the culture medium.In certain embodiments, the secreted monoterpenes may evaporate from theculture medium and can be captured as a gas composition in the headspaceof a vessel. In certain embodiments, monoterpenes can be recovered fromcellular components of the genetically modified microbial host cells.The monoterpenes in various phases can be recovered using knowntechniques in the art. For example, production and recovery techniquesare described in WO2007/139924, which is incorporated herein byreference in its entirety.

In some embodiments, a liquid organic phase comprising the myrcene maybe separated from the fermentation medium by centrifugation. In otherembodiments, a liquid organic phase comprising the myrcene separatesfrom the fermentation spontaneously. In yet other embodiments, a liquidorganic phase comprising the myrcene is separated from the fermentationby adding a deemulsifier and/or a nucleating agent into the fermentationreaction. Illustrative examples of deemulsifiers include flocculants andcoagulants. Illustrative examples of nucleating agents include dropletsof the myrcene itself and organic solvents such as dodecane, isopropylmyristate, methyl oleate, mineral oil, polyalphaolefins, and the like.In certain embodiment, the genetically modified microbial host cells canbe cultured in a production medium with an organic phase overlay (e.g.,10% or 50% overlay of isopropyl myristrate) to facilitate recovery.

In some embodiments, the myrcene is separated from other products thatmay be present in the organic phase. In some embodiments, separation isachieved using adsorption, distillation, gas-liquid extraction(stripping), liquid-liquid extraction (solvent extraction),ultrafiltration, and standard chromatographic techniques.

Myrcenes produced by host cells can be recovered using any of a varietyof methods including but not limited to chromatography, extraction,solvent extraction, membrane separation, electrodialysis, reverseosmosis, distillation, chemical derivatization, and crystallization.

Additional processing steps to improve myrcene quantification orisolation include but are not limited to breaking open the host cells.Suitable methods include but are not limited to vortexing, sonication,homogenization, and the use of glass beads. Other processing steps caninclude centrifugation to remove unwanted cell debris from thesupernatant.

Myrcene production can be readily quantified using well-known methodsknown in the art including but are not limited to gas chromatography(GC), gas chromatography-mass spectrometry (GC/MS), nuclear magneticresonance (NMR), RAMAN spectroscopy, optical absorption (UV/VIS),infrared spectroscopy (IR), high performance liquid chromatography(HPLC), liquid chromatography-mass spectrometry (LC/MS), ionchromatography-mass spectrometry, thin layer chromatography, pulsedamperometric detection, and UV-vis spectrometry.

In some embodiments, the myrcene is pure, e.g., at least about 40% pure,at least about 50% pure, at least about 60% pure, at least about 70%pure, at least about 80% pure, at least about 90% pure, at least about95% pure, at least about 98% pure, or more than 98% pure, where “pure”in the context of an myrcene refers to an myrcene that is free fromother terpenes or contaminants.

8. EXAMPLES 8.1 Construction of Nucleic Acid Constructs and Plasmids

This example describes methods for making nucleic acid constructs andplasmids useful in the generation and characterization of myrcenesynthase variants.

A high copy plasmid (2μ/leu2d plasmid) was used to express myrcenesynthases from different organisms. The 2μ/leu2d plasmid is described inErhart and Hollenberg, J. Bacteriol. 1983, 156(2): 625-635.

Plasmid pAM11613 was used for competition assays for tier I mutagenesis,and has a nucleotide sequence of SEQ ID NO: 33. Plasmid pAM11613 has thefollowing as main elements in addition to the yeast vector backbone: pUCorigin (bp 3218 to 2551); CYC1 terminator (bp 3595 to 3405); trichodienesynthase (“TDS”; bp 4729 to 3605); Gal1/10 promoter (bp 5403 to 4737);limonene synthase version A from Citrus limon (“LMSvA”; bp 5414 to7096); ADH1 terminator (bp 7262 to 7098); and Leu2d (bp 8107 to 9198).

Plasmid pAM11614 was used for competition assays for combinatoriallibrary of ObMS mutant, and has a nucleotide sequence of SEQ ID NO: 34.Plasmid pAM11614 has the following as main elements in addition to theyeast vector backbone: pUC origin (bp 2551 to 3218); CYC1 terminator (bp3405 to 3595); trichodiene synthase (“TDS”; bp 3605 to 4729); Gal1/10promoter (bp 4737 to 5403); limonene synthase version B from Citruslimon (“LMSvB”; bp 5414 to 7099); ADH1 terminator (bp 7101 to 7265); andLeu2d (bp 8110 to 9201).

Plasmid pAM2947 contains the F-CphI gene operably linked to pTDH3promoter, a kanmx4-marker, and the Cen-ARS. The nucleotide sequence ofplasmid pAM2947 is shown as SEQ ID NO: 35.

8.2 Microbial Host Strains

This example describes methods for making yeast strains used in thegeneration and characterization of myrcene synthase variants.

Yeast strain Y13203, derived from a wild-type Saccharomyces cerevisiaestrain (CEN.PK2), was used to express and screen myrcene synthases fromvarious organisms. The strain overexpresses the mevalonate pathway genesby chromosomally integrating mevalonate pathway genes (acetyl-CoAthiolase, HMG-CoA synthase, HMG-CoA reductase, mevalonate kinase,phosphomevalonate kinase, mevalonate pyrophosphate decarboxylase, andIPP isomerase gene) from S. cerevisiae under the control of GALpromoters. Additional information about the chromosomal integration ofthe mevalonate pathway genes and IPP isomerase and their sequences canbe found in U.S. Pat. Nos. 8,221,982 and 8,859,261, which areincorporated herein by reference in their entirety. The strain is alsoengineered to down regulate ERG20 gene expression by operably linkingthe ERG20 with promoter pCTR3 (Labbe and Thiele, Methods of Enzymology,vol. 306, pages 145-153).

Yeast strain Y21605 is derived from a wild-type Saccharomyces cerevisiaestrain (CEN.PK2). This strain is derived from strain Y13203. The straincontains ObMS nucleic acid (SEQ ID NO: 3) operably linked to promoterPgal1 and AgGPPS (SEQ ID NO: 8) operably linked to promoter Pgal10 on a2μ/leu2d plasmid. The strain also comprises the chromosomally integratedmevalonate pathway genes (acetyl-CoA thiolase, HMG-CoA synthase, HMG-CoAreductase, mevalonate kinase, phosphomevalonate kinase, and mevalonatepyrophosphate decarboxylase, and IPP isomerase gene) from S. cerevisiaeunder the control of GAL promoters. The strain is also engineered todown regulate ERG20 gene expression by operably linking the ERG20 withpromoter pCTR3.

Myrcene screening host strain Y21704 was used to screen GPPSs fromvarious organisms. The strain is derived from strain Y13203 and furthercomprises a GB1 expression tagged ObMS nucleic acid sequence operablylinked to promoter Pgal1 on a leu2d plasmid. The GB1 expression tag isdescribed in Chen and Patel, Biochem. Biophys. Res. Comm. 317(2):401-405 (2004).

Yeast strain Y10566 was used in a competition assay with plasmidspAM11613 and pAM11614. The strain is derived from a wild-typeSaccharomyces cerevisiae strain (CEN.PK2). The strain comprises thenucleic acids described above for strain Y13203 and further comprisestwo copies of AgGPPS gene (SEQ ID NO: 8).

Yeast strain X100 was used to express 1×ObMS, 5×ObMS, and 14×ObMSnucleic acids and to compare their myrcene titer. The strain is derivedfrom a wild-type Saccharomyces cerevisiae strain (CEN.PK2). The straincomprises nucleic acids described above for Y13023 and further comprisestwo copies of SaGPPS (SEQ ID NO: 7) operably linked to pGAL1 promoter,ERG20 operably linked to pMAL1 promoter, and landing pads for myrcenesynthase nucleic acids.

8.3 Cell Density Measurements

This example describes methods for determining the cell density of amicroorganism culture.

The amount of microorganism per liter of fermentation, or the density ofmicroorganism, can be measured by measuring the weight of microorganismisolated from a given volume of the fermentation medium. A commonmeasure is the dry weight of cells per liter of fermentation medium.Another method which can be used to monitor the fermentation while it isprogressing is by a measurement of the optical density of the medium. Acommon method is to measure the optical density at a wavelength of 600nm, referred to the OD₆₀₀, or the OD. The OD can be correlated to thedensity of a specific type of organism within a specific medium, but thespecific relationship between OD and amount of microorganism per volumemay not generally be applicable across all types of organisms in alltypes of media. A calibration curve can be created by measuring the ODand the dry cell weight over a range of cell densities. In some cases,these correlations can be used in different fermentation of the same orsimilar microorganisms in the same or similar media.

An exemplary method for determining the cell density (OD₆₀₀) of a yeastcell culture is as follows. An 8 μL sample of a cell culture is combinedwith 92 μL of Triton OD Diluent (20 g/L Triton X-114, 200 mL/L PEG 200,200 mL/L 100% ethanol, rest water) in a clear 96-well plate, thesolution is agitated at 1,000 RPM for 6 minutes, and the OD₆₀₀ wasdetermined by measuring absorbance at 600 nm on an M5 spectrophotometer(Molecular Devices, Sunnyvale, Calif.).

8.4 GC Methods to Determine the Proportion of Myrcene in a Mixture ofMonoterpenes and its Titer

This example describes an exemplary gas chromatography (GC) based methoduseful for determining the area % product purity and myrcene titers ofyeast cell cultures.

The area % product profile purity for samples containing myrcene weredetermined using an Agilent Gas Chromatograph with Flame IonizationDetection (GC-FID). The GC-FID method parameters are outlined in Table1A. The area % product profile purity is a purity measure where the %purity is the area due to myrcene expressed as a percentage of the totalmonoterpenes area, and is a measure of the purity of the product profileof a particular enzyme.

TABLE 1A The GC-FID parameters used to obtain the area % product profilepurity of myrcene in samples. Oven Initial Temp, (° C.) 40.0 InitialHold, (min) 8.0 Rate 1, (° C./min) 5.0 Temp 1, (° C.) 150.0 Final Time1, (min) 30.0 Rate 2, (° C./min) 50.0 Final Temp, (° C.) 320 Final Time2, (min) 31.4 Rate 3, (° C./min) 0.0 Final Temp, (° C.) 320 Final Time3, (min) 36.4 Rate 4, (° C./min) OFF Runtime, (min) 36.4 Column AgilentHP-1 Dimensions 50 m × 0.20 mm, 0.11 μm film

The monoterpene (C10) retention time window on the GC-FID chromatogramis defined as between 10.0 and 23.0 minutes. No monoterpenes were shownto elute earlier than 10.0 minutes and later than 23 minutes asdetermined by testing terpene standards and by GC-MS analysis ofsynthase products (presence of molecular ion 136). In addition, unknownpeaks observed in the analyzed samples were excluded as non-terpenes ifthey were detected in the negative control. The negative control was astrain that had a nonfunctional myrcene synthase.

For determining myrcene titer, GC-FID with an LTM column was used withan external standard calibration. The GC-FID parameters used to measuremyrcene amounts are outlined in Table 1B. The external standardcalibration was prepared on a weight by volume basis. A known amount ofmyrcene was diluted in ethyl acetate, and serial dilutions of 10-200mg/L were prepared and used to calibrate the instrument.

TABLE 1B The GC-FID parameters used to obtain the myrcene amounts OvenMach, LTM Initial Temp, (° C.) 80 Initial Hold, (min) 0.15 Rate 1, (°C./min) 15 Temp 1, (° C.) 120 Hold Time 1, (min) 0 Rate 2, (° C./min)300 Final Temp, (° C.) 320 Hold Time 2, (min) 3.0 Final Time, (min) 6.48Runtime, (min) 6.48 Column Agilent, Agilent DB-1MS- LTM Dimensions 10 m× 0.10 mm, 0.10 μm film

8.5 Headspace Analysis to Determine Myrcene Titer

This example describes an exemplary method useful for quantification ofmyrcene in the gas phase in the well headspace of a plate.

For a competition assay where a myrcene synthase variant sequence and acontrol enzyme, (R)-limonene synthase, sequence were cloned on the sameplasmid, both myrcene and limonene were quantified via the headspaceanalysis. Strains were grown in sealed 2.2 ml 96-well plates, afterwhich volatile myrcene and limonene present in the well headspace wereanalyzed by Headspace Gas Chromatography/Flame Ionization Detection(GC/FID). GC/FID system is composed of Agilent 7890 gas chromatographwith FID detector and a Gerstel MPS autosampler. One hundred microliterof the headspace gas was injected into GC, and samples were separatedthrough Agilent HP-5 P/N 1909J413 column (7 m×0.200 mm, 0.33 μm film)using hydrogen as the carrier gas. The temperature of GC oven was set to55° C. For quantification of myrcene, calibration standards with knownconcentrations of myrcene and/or limonene in IPM overlay were prepared,filled to 2.2 ml plates, sealed, and ran in parallel with the samples.

8.6 Screening Wild-Type Myrcene Synthase Genes from Various Species

This example describes screening wild-type myrcene synthase genes fromseveral different species to select a myrcene synthase gene suitable forexpression in yeast cells.

A number of myrcene synthase genes from different organisms that wereeither biochemically characterized in the literature or putativelyannotated as myrcene synthases were selected for screening for suitablemyrcene synthase genes for heterologous expression in yeast host cells.As shown in Table 2 below, these genes include those obtained from Piceaabies (Martin et al. (2004) Plant Physiol. 135, 1908-1927); Abiesgrandis (Bohlmann et al. (1997) JBC 272, 21784); Ocimum basilicum(Irijima et al. (2004) Plant physiol. 136, 3724-3736); Quercus ilex(Fischbach et al. (2001) Eur. J. Biochem. 268, 5633-5638); Antirrhinummajus (Dudareva et al. (2003) Plant Cell 15, 1227-124); Alstroemeriaperuviana (Aros et al. (2012) J. Exp. Botany 63, 2739-2752); andMedicago truncatula. The nucleotide sequences are also available fromNCBI GenBank.

For each gene, two different codon optimized sequences were designedaccording to standard protocol using software provided by Integrated DNATechnologies (Coralville, Iowa), http://www.idtdna.com/CodonOpt,selecting Saccharomyces cerevisiae as the codon organism. Two examplesof codon optimized sequences are shown as SEQ ID NO: 3 (Ocimum basilicummyrcene synthase) and SEQ ID NO: 36 (Quercus ilex myrcene synthase). Thetesting was carried out in Saccharomyces cerevisiae strain Y13203 withboth myrcene synthase nucleic acid and AgGPPS nucleic acid (SEQ ID: 6;codon optimized) expressed on a high copy plasmid 2μ/leu2d.

Strains comprising different myrcene synthase genes were picked fromcolonies on an agar plate into 2 ml of 2% sucrose Bird Seed Media (BSM,originally described by van Hoek et al., Biotechnology andBioengineering 68(5), 2000, pp. 517-523) in a falcon tube and incubatedat 30° C. for 24 hours with shaking. Strain variants were thensubcultured to 0.08 OD₆₀₀ in 10 ml of 4% galactose BSM, 125 μM CuSO₄ ina 125 ml baffled flask with 10 ml isopropyl myristate (IPM) as anoverlay. Samples were taken at 24 hour, 48 hour, or 72 hour as needed.Myrcene titer was determined by diluting 100 μl of IPM taken from thesample at desired time points into 900 μl of ethyl acetate in a glass GCvial. Samples were vortexed, and were analyzed by gas chromatography(GC) as described in Example 7.4. The cell density was determined atOD₆₀₀ by diluting 100 μl of broth into 900 μl of sterile water in acuvette. Cuvettes were vortexed and the cell density at OD₆₀₀ wasassayed using a spectrophotometer.

TABLE 2 The myrcene production from various strains comprising differentmyrcene synthase genes is shown below: Myrcene Organism Enzymeproduction Myrcene (common name) name in 72 h purity Uniprot SEQ ID NOS.Ocimum basilicum (Basil) ObMS ~1 g/L 89% Q5SBP1 SEQ ID NO: 3 Quercusilex (Holly oak) QiMS 200 mg/L 91% Q93X23 SEQ ID NO: 36 Picea abies(Norway spruce) PaMS 50 mg/L 89% Q675K9 Abies grandis (Grand fir) AgMSNo Inactive Q24474 myrcene Aegilops squarrosa (Goatgrass) AsMS NoInactive M8AXZ3 myrcene Alstroemeria peruviana ApMS 15 mg/L Low activityI3IRM3 (Peruvian lily) Antirrhinum majus AmMS 13 mg/L Low activityQ84NDO (Snapdragon) Medicago truncatula MtMS1 No Likely not a A0RZI3(Barrel clover) myrcene MS Medicago truncatula MtMS2 No Likely not aG7IRJ6 (Barrel clover) myrcene MS

As summarized in Table 2, the notable myrcene synthases are ObMS (˜1g/L), QiMS (200 mg/L), and PaMS (50 mg/L), from which myrcene productionwas observed. Other myrcene synthases shown in Table 2 produced eitherinactive or low activity myrcene synthase. Two of them (MtMS1 and MtMS2)produced no myrcene, indicating that they are likely not a myrcenesynthase. When the ObMS amino acid sequence was aligned with othermyrcene synthase sequences in Table 2, the ObMS amino acid sequenceshares less than 50% identity with other myrcene synthase amino acidsequences (analysis according to Clone Manager Suite, method:FastScan—Max Qual (Cons N).

Monoterpenes produced from the host strains expressing ObMS, QiMS, andPaMS were analyzed using GC-MS and GC-FID analysis as described inExample 7.4. The results show that QiMS and PaMS appear to produce anequal or higher proportion of myrcene in the mixture of monoterpenes(i.e., myrcene purity profiles) than ObMS. However, as shown in Table 2,ObMS expressed in genetically modified microbial host cells generated atleast five fold higher myrcene production after 72 hours of culturecompared to another myrcene producer (i.e., QiMS). It is noted that alow level of geraniol was observed but was not included as an impurityin the calculation of myrcene purity because it was likely generatedfrom myrcene synthase-independent hydrolysis of GPP in yeast.

FIG. 3A shows a comparison of GC-FID traces of myrcene and otherco-products produced by yeast host cells comprising ObMS (trace in themiddle) and QiMS (trace at the bottom). As shown by the differences inthe two traces, each myrcene synthase exhibits a distinct productprofile. In particular, the ObMS trace indicates that the monoterpenesproduced from genetically modified microbial host cells expressing ObMSinclude α-terpinene, γ-terpinene and 4-terpineol, which are not presentin the monoterpenes produced from yeast cells expressing QiMS. A numberof samples comprising yeast host cells comprising other myrcenesynthases were analyzed by GC-FID. Similar to QiMS, other myrcenesynthases did not produce α-terpinene, γ-terpinene, 4-terpineol, orother monoterpene co-products.

8.7 Monoterpene Product Profile Produced from Ocimum basilicum MyrceneSynthase

In this example, the monoterpene product profile of ObMS determined froma GC-MS analysis is described in detail.

Y21605 strain comprising the ObMS nucleic acid (SEQ ID NO: 3) was grownfor 2 days pre-culture in a falcon tube containing 2 ml of BSM 2%sucrose medium and incubated at 30° C. with shaking. For production, thestrain was grown for 96 hours at 30° C. in a 125 ml unbaffled shakeflask containing 10 ml BSM 4% galactose and 125 μM CuSO₄ with 10 ml ofIPM as an overlay. 1 ml of IPM was sampled from the overlay and spundown to pellet any biomass present. A 500 μl of clarified IPM wasdiluted twice in 500 μl of ethyl acetate in a GC vial and was analyzedby GC-MS analysis using Agilent 7890 gas chromatograph with massspectrometer.

The sample was analyzed using GC-MS as follows. HP-1, 50 m×0.2 mm×0.11um column was used for myrcene analysis. Briefly, 1 μl or 3 μl of sampleat about 0.5 g/L was injected on the column and the followingtemperature gradient was applied: 40° C. with hold for 8 minutes; rampat 5° C./min to 150° C.; followed by a ramp at 120° C. to 320° C. withhold for 5 minutes to bake out the column. Helium is used as a carriergas with constant flow at 1.5 ml/min. Inlet is set to 250° C. with the10:1 split ratio. MS Source is set to 230° C. and MS quad to 15° C.Solvent delay was set to 4 min, EMV Mode to Gain Factor with Gain Factorto 15.

Data was analyzed by NIST 2009 and Wiley 9th Edition Libraries usingboth Kovats Retention Index (KI) and compound MS trace, with proposedassignments given in Table 3. KI is relative retention value based on ascale defined by the elution of a series of n-alkanes and calculatedusing the following equations:

-   -   For temperature programmed chromatography, the Kovats index is        given by the equation

$I = {100 \times \left\lbrack {n + {\left( {N - n} \right)\frac{t_{r{({unknown})}} - t_{r{(n)}}}{t_{r{(N)}} - t_{(n)}}}} \right\rbrack}$

-   -   Where:    -   I=Kovats retention index,    -   n=the number of carbon atoms in the smaller n-alkane.    -   N=the number of carbon atoms in the larger n-alkane.    -   t_(r)=the retention time.

Available authentic standards of compounds tentatively identified bylibrary match were analyzed for definitive conformation of peakassignment, as summarized in Table 3. See also, FIG. 4 for molecularstructures of compounds associated with peak assignments.

TABLE 3 TABLE 3 illustrates calculation of KI index for selected peakswith MW 136 (C10 terpene) and 154 (C10 terpene alcohol). Matchingcompounds are selected from NIST library based on fragmentation patternand KI. “?” stands for tentative assignment due to low library score.peak RT tr tr tr KI KI Library [min.] n N unknown n N calculateddatabase match 12.544 9 10 12.544 11.53 15.903 923.2 928-929 α-Thujene ?14.327 9 10 14.327 11.53 15.903 964.0 964-975 Sabinene 15.315 9 1015.315 11.53 15.903 986.6 979-981 Myrcene 16.101 10 11 16.101 15.90319.562 1005.4 1008-1017 α-Terpinene 16.56 10 11 16.56 15.903 19.5621018.0 1020 (+)-Limonene 17.375 10 11 17.375 15.903 19.562 1040.21032-1041 β-Ocimene 17.647 10 11 17.647 15.903 19.562 1047.7 1047-1053γ-Terpinene 17.729 10 11 17.729 15.903 19.562 1049.9 1050 (E)-sabinenehydrate ? 18.759 10 11 18.759 15.903 19.562 1078.1 1068-1090(Z)-sabinene hydrate ? 19 10 11 19 15.903 19.562 1084.6 1081-1082β-Linalool 21.338 11 12 21.338 19.562 22.74 1155.9 1160-1175(−)-4-Terpineol

TABLE 4 Table 4 shows KI values for tested standards and correspondingvalues for peaks detected in the analyzed sample. Standards for testingwere selected based on results from Table 3. KI of KI of RT of standardunknown in Standard name standard [min.] sample Sabinene 14.284 963 964Myrcene 15.215 987 987 α-Terpinene 16.069 1005 1005 Limonene 16.534 10181018 β-Ocimene 17.359 1040 1040 γ-Terpinene 17.63 1048 1048 β-Linalool18.987 1085 1085 4-terpineol 21.319 1156 1156

TABLE 5 Table 5 illustrates area % purity for analyzed myrcene sample(i.e., relative monoterpenes in a sample composition based on area %)injected at 3 μl and 1 μl. For area % calculation, area of all peakswith MW 136 (C10 terpene) and 154 (C10 terpene alcohol) were added to100% (assuming the same signal response for all compounds). Peaks witharea % less than 0.5 % were rejected and area % was re-calculated forremaining compounds. Area %, 3 μl Area %, 1 μl Compound name RTinjection injection α-Thujene (tentative) 12.544 0.51 NA Sabinene 14.3270.98 0.80 Myrcene 15.315 89.09 92.01 α-Terpinene 16.101 0.90 0.67Limonene 16.56 1.01 0.54 β-Ocimene 17.375 1.21 0.91 γ-Terpinene 17.6471.06 1.00 (E)-sabinene hydrate (tentative) 17.729 0.54 NA (Z)-sabinenehydrate (tentative) 18.759 1.13 0.98 β-Linalool 19.000 1.17 0.764-terpineol 21.338 2.42 2.32

A GC-MS analysis of an ObMS myrcene sample extracted from the broth ofY21605 revealed six other C10 terpenes and four C10 terpene alcohols asminor components in addition to myrcene. See FIG. 3B. The main impurityamong the minor co-products is 4-terpineol which is present at about2.3%. In FIG. 3B, peak 1 represents thujene; peak 2 represents sabinene;peak 3 represents myrcene; peak 4 represents α-terpinene; peak 5represents limonene; peak 6 represents ocimene; peak 7 representsγ-terpinene; peak 8 represents (E)-sabinene hydrate; peak 9 represents(Z)-sabinene hydrate; peak 10 represents β-linalool; and peak 11represents 4-terpineol. The molecular structures of all ten co-productsare shown in FIG. 4 . The relative area % for each co-product wasmeasured at two different injection volumes of the sample, with thehigher injection giving higher impurity levels (Table 5). The myrcenepurity was again measured at 89-92% based on the peak areas, consistentwith the previous result. GC-MS analyses of other samples derived fromhost cells genetically modified with myrcene synthase variants describedin Examples 7.9 to 7.11 below exhibited substantially similar myrcenepurity levels and other co-product peaks as shown in FIG. 3B (data notshown).

8.8 Screening Wild-Type Geranyl Pyrophosphate Synthase Genes fromVarious Organisms for Co-Expression with a Myrcene Synthase

This example describes screening wild-type geranyl pyrophosphatesynthase genes from various organisms to select for a geranylpyrophosphate gene suitable for co-expression with a myrcene synthase inyeast host cells.

Several GPPSs, including both homodimeric and heterodimeric enzymes,were selected for screening. See Table 6 below. For each gene, twodifferent codon optimized sequences were designed according to standardprotocol using software provided by Integrated DNA Technologies(Coralville, Iowa) at http://www.idtdna.com/CodonOpt, selectingSaccharomyces cerevisiae as the codon organism. For initial testing,each sequence was cloned via single-copy integration into yeast strainY13203 with ObMS expressed on a high copy plasmid 2μ/leu2d. Myrceneproduction (as measured by GC) in these strains is dependent on theactivity of GPPS—a more active GPPS diverts more carbon from sugar tohigher level of GPP for ObMS, leading to higher myrcene titers. Severalstrains were also constructed with (R)-limonene synthase (ClLMS fromCitrus limon), an enzyme with higher activity in yeast than ObMS, inplace of ObMS, and limonene production was compared with myrcene to helpdiagnose whether a myrcene synthase is limiting.

The previous experiments with AgGPPS showed that one copy of AgGPPS wasnot sufficient to support normal strain growth and only supported lowlevel of myrcene production (data not shown). It was therefore unclearprior to the screening whether integrating a single copy of GPPS wouldprovide sufficient activity for the purpose of this screening. However,the single-copy integration approach could potentially allowidentification of the most active GPPSs faster and more definitivelythan a plasmid-based approach where weaker GPPSs are compensated byhigher copy numbers. Indeed, although AgGPPS containing strain did notgrow very well and produced a relatively low amount of myrcene, it wasfound that a homodimeric bacterial GPPS, Streptomyces aculeolatus, wasable to support robust strain growth as shown in Table 6.

TABLE 6 Summary of GPPSs screening results. Activity is defined asamount of strain growth in plates with GPPS integrated as a single copy.Enzyme Activity (with a Organism (common name) Name Gene Accession Nos.(Notes) single copy) Abies grandis (Grand fir) AgGPPS AF513112.1 LowStreptomyces aculeolatus SaGPPS ABS50454 (Biochemically verified to Highbe a GPPS) Ips pini (bark beetle) IpGPPS AY953508 (GPPS and MS Lowbifunctional enzyme; low activity as GPPS) Catharanthus roseus CrGPPSJX417185 No (Madagascar periwinkle) Humulus lupulus (European hop)HlGPPS ACQ90682/ ACQ90681 No (Heterodimer) Glycine max (Soybean) GmGPPSABY90133 No Mangifera indica (Mango) GPPS1 AFJ52721 No Mangifera indica(Mango) GPPS2 AFJ52722 No Medicago sativa (Alfalfa) MsGPPS AEL29573 NoPhalaenopsis bellina (Orchid) PbGPPS ABV71395 No Picea abies (Norwayspruce) PaIDS1 GQ369788 No Salvia miltiorrhiza (Chinese sage) GPPSAEZ55677 No Vitis vinifera (Grape) VvGPPS AAR08151 No

The myrcene production was also measured in strain Y21704. Myrcenescreening host strain Y21704 containing a Pgal1 driven ObMS on a leu2dplasmid was unable to reach maximum OD₆₀₀ in culturing conditions wheninduced on galactose with 125 μM CuSO₄ in the absence of a functionalGPPS. As such, nonfunctional GPPS variants were determined by lack ofgrowth of their host strain in a 96 well plate model. Strain variants,each comprising a GPPS gene from different organisms, were picked fromsingle colonies on an agar plate into a 96 well plate containing 360 μlof 2% sucrose BSM and incubated for 24 hours at 30° C. with shaking. Forproduction, 6 μl of each well was then subcultured into a new 96 wellplate containing 360 μl of 4% galactose BSM and incubated for 72 hoursat 30° C. with shaking. OD₆₀₀ measurement samples were taken at 72hours, and functional GPPS variants determined by positive growth. Thissubset of functional GPPS variants integrated into Y21704 was tested formyrcene production in 125 ml baffled shake flasks as described above inExample 7.6. The samples were analyzed using the GC analysis methoddescribed in Example 7.4.

FIG. 5 illustrates the comparison of myrcene production by twoGPPSs—SaGPPS and AgGPPS. The codon optimized nucleotide sequence forSaGPPS is shown as SEQ ID NO: 6. The codon optimized nucleic acidsequence for AgGPPS is shown as SEQ ID NO: 8. As shown in FIG. 5 , thebacterial GPPS derived from Streptomyces aculeolatus supported at leastthree fold increase in myrcene production compared to the AgGPPS derivedfrom plant species. Thus, the bacterial SaGPPS was selected as a GPPSfor co-expression with ObMS in other experiments.

8.9 Generation of Myrcene Synthase Variants—Tier I Mutagenesis

This example describes methods for generating libraries of myrcenesynthase variants and a competition assay to rank improvement in myrcenesynthase activity for each variant over the parent sequence.

In a competition assay, each variant sequence is cloned into plasmidpAM11613. A control enzyme, (R)-limonene synthase from Citrus limon(CILSvA), is also expressed on the same plasmid as a test myrcenesynthase variant, and the two synthases compete in a microbial host cellfor the same substrate (GPP) for the production of myrcene and limonene,respectively. Strains containing the competition plasmid co-producesmyrcene and limonene, and the ratios of myrcene and limonene fordifferent myrcene synthase variants are used as the readout for therelative activity of these enzymes. The myrcene synthase variants areidentified when they outperform their parent in competing against alimonene synthase for converting GPP to myrcene as opposed to limonene(i.e., higher myrcene to limonene ratios than that of its parent).

To design a mutagenesis library, an alignment of protein sequences ofObMS and several other terpene synthases were created. The residuesfound to generate beneficial mutations from those terpene synthases,“hot spots,” as well as the proposed active site residues were overlaidonto the alignment. Potential hot spots for ObMS were predicted andranked in order of importance based on the conservation of the region orthe residues, the sizes of hits previously identified, and the number ofsynthases that the residue was found to be beneficial. A total of 47 hotspots were selected.

A saturation mutagenesis library at each of the 47 amino acid positionsusing a NDT degenerate codon was constructed, leading to 12 possibleamino acid changes at the positions. Site-directed mutagenesis librarywas created by polymerase chain reaction (PCR) mutagenesis using thewild-type myrcene synthase sequence encoding ObMS as template. Mutationswere introduced using degenerate NDT codon to convert the residue at theidentified position from its wild-type amino acid sequence to a mixedpopulation of 12 possible amino acid sequences (Phe, Leu, Ile, Val, Tyr,His, Asn, Asp, Cys, Arg, Ser, Gly). Internal degenerate primers used tointroduce mutations to residue positions 213, 381, 389, 404, 439, 484,482, 528 and 543, as well as flanking primer sequences are listed inTable 7.

TABLE 7The forward and reverse primers used to introduce mutations into theObMS are shown below. The first column indicates the amino acidpositions of SEQ ID NO: 2 (ObMS amino acid sequence) and forwardor reverse primers, the second column indicates the sequence ID numbers,and the third column shows the nucleotide sequences of the primers. aapositions SEQ ID NO. Sequence 213-IF SEQ ID NO: 9TGGTTCTTAGATGCTTATGCTAGCAGACC 213-IR SEQ ID NO: 10GGTCTGCTAGCATAAGCATCTAAGAACCAAHNGGCCTCCAGCCTTTGA ATCCG 381-IFSEQ ID NO: 11 CGTGGCTGGATTTGGTTGAAGCATATNDTGTTGAGGCAAAGTGGTTCC ACGAT381-IR SEQ ID NO: 12 ATATGCTTCAACCAAATCCAGCCACG 389-IF SEQ ID NO: 13TATTTTGTTGAGGCAAAGTGGTTCCACNDTGGATATACTCCAACTCTAG AAGAATATCTC 389-IRSEQ ID NO: 14 GTGGAACCACTTTGCCTCAACAAAATATGC 404-IF SEQ ID NO: 15CTAGAAGAATATCTCAACAATTCGAAGNDTACAATAATTTGTCCTGCAA TAGTCTCAGAA 404-IRSEQ ID NO: 16 CTTCGAATTGTTGAGATATTCTTCTAGAGT 439-IF SEQ ID NO: 17GAGAGCATATACAAATATCATGACATCCTTNDTCTTTCCGGAATGCTTG CAAGGCT 439-IRSEQ ID NO: 18 AAGGATGTCATGATATTTGTATATGCTCTC 528-IF SEQ ID NO: 19CTCGGAAGAGTGGCTAATTTTGTGTATGTGNDTGGAGATGGTTTTGGA GTGCAACACTC 528-IRSEQ ID NO: 20 CACATACACAAAATTAGCCACTCTTCCGAG 543-IF SEQ ID NO: 21GTGCAACACTCAAAAATACATCAACAANDTGCTGAATTACTGTTTTACC CATATCAGTAA 543-IRSEQ ID NO: 22 TTGTTGATGTATTTTTGAGTGTTGCACTCC 482-IF SEQ ID NO: 23ACGCCTCAGAGGAGGAGGCANDTGAGCACATCAGATTTCTTATGCGG GAG 482-IR SEQ ID NO: 24TGCCTCCTCCTCTGAGGCGT 484-IF SEQ ID NO: 55CTCAGAGGAGGAGGCACGTGAGNDTATCAGATTTCTTATGCGGGAGG CGT 484-IR SEQ ID NO: 56CTCACGTGCCTCCTCCTCTGAG 552-IF SEQ ID NO: 25AAATGGCTGAATTATTGTTTTACCCATACNDTTAAGCTAGCTAAGATCC GCTCTAACCGA 552-IRSEQ ID NO: 26 GTATGGGTAAAACAATAATTCAGCCATTTG 544-IF SEQ ID NO: 27TTCGGTGTCCAACACTCTAAGATTCACNDTCAAATGGCTGAATTATTGT TTTACCCATAC 544-IRSEQ ID NO: 28 GTGAATCTTAGAGTGTTGGACACCGAAACC AM-405 SEQ ID NO: 37CGTCAAGGAGAAAAAACCCCGGATCCATGGTTGAACCCCGACGC AM-168 SEQ ID NO: 38GCAAGGTTTTCAGTATAATGTTAC 27-IF SEQ ID NO: 57TCCAAGGAAGAACGTCATTTGGAAAGAAAG 27-IR SEQ ID NO: 58TCTTTCCAAATGACGTTCTTCCTTGGAAHNGTTGTTGTTCAAGGATTGA ATGTAATTAAA 28-IFSEQ ID NO: 59 AAGGAAGAACGTCATTTGGAAAGAAAGGCT 28-IR SEQ ID NO: 60CTTTCTTTCCAAATGACGTTCTTCCTTAHNATGGTTGTTGTTCAAGGATT GAATGTAATT 207-IFSEQ ID NO: 61 CAAAGATTGGAGGCCAAATGGTTCTTGG 207-IR SEQ ID NO: 62CAAGAACCATTTGGCCTCCAATCTTTGAHNTCTCCAATGCAAAGGTAAC TCCAAAGAGTG 222-IFSEQ ID NO: 63 CCAGATATGAACCCAATTATTTTCGAATTG 222-IR SEQ ID NO: 64CAATTCGAAAATAATTGGGTTCATATCTGGAHNAGAGGCGTAGGCATC CAAGAACC 342-IFSEQ ID NO: 65 AACCAATTGCCATCTTACATGCAATTGNDTTATTTGGCCATTTATAACTTCGTCTCCGAA 342-IR SEQ ID NO: 66 CAATTGCATGTAAGATGGCAATTGGTTGAT 347-IFSEQ ID NO: 67 TCTTACATGCAATTGTGCTATTTGGCCATTNDTAACTTCGTCTCCGAATTGGCTTACGA 347-IR SEQ ID NO: 68 AATGGCCAAATAGCACAATTGCATGTAAGA 382-IFSEQ ID NO: 69 TCTTGGTTGGATTTGGTTGAAGCTTATTTCNDTGAAGCCAAGTGGTTCC ACGACG382-IR SEQ ID NO: 70 GAAATAAGCTTCAACCAAATCCAACCAAGA 390-IF SEQ ID NO: 71TTGAAGCCAAGTGGTTCCACGACNDTTACACTCCAACTTTGGAAGAATA CTTGAAC 390-IRSEQ ID NO: 72 GTCGTGGAACCACTTGGCTTCAA 401-IF SEQ ID NO: 73ACTCCAACTTTGGAAGAATACTTGAACNDTTCTAAGATTACTATCATTT GTCCAGCCATC 401-IRSEQ ID NO: 74 GTTCAAGTATTCTTCCAAAGTTGGAGTGTA 428-IF SEQ ID NO: 75TTTGCCAACTCTATCGATAAGACTGAANDTGAATCCATTTACAAGTATC ACGACATTTTG 428-IRSEQ ID NO: 76 TTCAGTCTTATCGATAGAGTTGGCAAAAGC 466-IF SEQ ID NO: 77GATGAAGCGTGGTGACGTTGCTAAGNDTATTCAATGTTACATGAAGGA ACACAACGCC 466-IRSEQ ID NO: 78 CTTAGCAACGTCACCACGCTTCATC 505-IF SEQ ID NO: 79CTGCCGCTGCTGCCGATGACNDTCCATTTGAATCTGACTTGGTTGTTGG TGC 505-IRSEQ ID NO: 80 GTCATCGGCAGCAGCGGCAG 514-IF SEQ ID NO: 81GACTGTCCATTTGAATCTGACTTGGTTGTTNDTGCTGCCTCCTTGGGTA GAGTC 514-IRSEQ ID NO: 82 AACAACCAAGTCAGATTCAAATGGACAGTC 517-IF SEQ ID NO: 83CTGACTTGGTTGTTGGTGCTGCCNDTTTGGGTAGAGTCGCTAACTTCGT CTAC 517-IRSEQ ID NO: 84 GGCAGCACCAACAACCAAGTCAG 524-IF SEQ ID NO: 85GCCTCCTTGGGTAGAGTCGCTAACNDTGTCTACGTTGAGGGTGATGGT TTC 524-IRSEQ ID NO: 86 GTTAGCGACTCTACCCAAGGAGGC 527-IF SEQ ID NO: 87CTTGGGTAGAGTCGCTAACTTCGTCTACNDTGAGGGTGATGGTTTCGG TGTC 527-IRSEQ ID NO: 88 GTAGACGAAGTTAGCGACTCTACCCAAG

To introduce mutations at the identified position, two PCR reactionswere performed with the 5′ external forward primer (AM-405) and internalreverse primers (IR), and internal forward primers (IF) and the 3′external reverse primer (AM-168), respectively, creating two overlappingfragments of the myrcene synthase sequence. The primer sequences areshown in Table 7. All PCR reactions were performed with Phusion®High-Fidelity DNA Polymerase according to manufacturer's manual.

To create the mutagenesis library in yeast, plasmid pAM11613 wasdigested with BamHI and NheI, and the digested vector backbone waspurified. One microliter of each PCR fragment was mixed with 15 ng ofdigested pAM11613, and gap repaired into yeast strain Y10566. Twelverandom clones from selected transformations were sequenced to confirmthat the library contained an appropriate diversity and frequency ofmutations at the desired residue position.

To screen for improved myrcene synthase activity, 36 yeast clones foreach residue position were inoculated into wells of a 96-well plate in360 μl of the preculture media (Bird Seed Medium containing sucrose 14g/L, maltose 7 g/L, and lysine 1 g/L), and grown at 30° C. for two daysby shaking at 1000 rpm. Then 3 μl of culture was subcultured into 2.2 ml96-well deep well plates containing 75 μl of production media (Bird SeedMedium containing galactose 4% and 125 μM CuSO₄). The plates were thenfoil sealed with a heat sealer (e.g., PlateLoc Thermal MicroplateSealer, Agilent Technologies) and grown at 30° C. for three days byshaking at 1000 rpm.

The GC headspace assay described in Example 7.5 was used to quantifymyrcene produced in the sealed plates at the end of growth andproduction. Headspace gas of the wells was injected directly into GC,and the peak areas of myrcene (produced by myrcene synthase mutants) andlimonene (produced by limonene synthase present in vector pAM11613) werequantified. The ratio of myrcene peak area to limonene peak area wascalculated for each yeast clone in the plates, and compared to that ofthe yeast clone expressing the wild-type myrcene synthase having thesequence of SEQ ID NO: 2. The yeast clone with an increasedmyrcene/limonene ratio was identified, and its myrcene synthase sequencewas amplified and sequenced.

A total of nineteen beneficial mutations identified from screening thesaturation mutagenesis library of 1×ObMS were ported onto 5×ObMS, thenew codon variant that is approximately 5 times better than 1×ObMS. Thenineteen mutants in the 1×ObMS background exhibited at least about 10%improvement in activity compared to their parent 1×ObMS. As summarizedin Table 8, about 10-70% improvements in activity were obtained for themajority of mutants over the new parent 5×ObMS, a level of improvementssimilar to that observed with 1×ObMS. The myrcene synthase variants withthe highest activity, 5×ObMS_M543I and 5×ObMS_E528D exhibited more than8-fold improvement over the 1×ObMS.

TABLE 8 Beneficial mutations are portable from 1xObMS to 5xObMS.Competition ratios were normalized to that of 5xObMS. The CVs werecalculated from 6 replicates. Beneficial mutations selected to beincluded in the combinatorial library were marked with an “X”. CombResidue Synthase Improvement CV library 5xObMS 0.0% 4.4% K213C 9.7% 2.4%K213H 34.9% 5.3% X 213 K213R 14.4% 2.8% K213V 9.9% 0.7% 381 F381L 9.2%5.2% X D389G 31.7% 5.2% X 389 D389S 20.7% 3.2% 404 1404V 40.9% 4.2% X439 Y439L 19.9% 4.7% X R482C 23.8% 1.5% R482D 43.7% 2.9% R482H 38.1%5.3% 482 R482I 61.2% 5.8% X R482L 50.3% 4.7% R482N 43.2% 5.6% R482V62.2% 4.7% 484 H484Y 2.4% 3.9% 528 E528D 68.5% 3.6% X 543 M543I 69.7%3.8% X

In order to identify additional beneficial mutations that improve theactivity of 5×ObMS enzyme, a second saturation mutagenesis library wasbuilt and screened with the 5×ObMS as parent. To construct the library,100 amino acid residues were selected to introduce mutations using NDTdegenerate primers as described above. The primer sequences aresummarized in Table 7. Selection of the 100 amino acid residues werebased on two criteria: 1) additional “hot spots” from other terpenesynthases (described above) that were not included in the firstmutagenesis library; and 2) an ObMS homology model. Residues wereselected that are located between 8 and 12 Å from the active site. Thislibrary was screened using the same protocol as described above. A totalof 29 beneficial mutations at 16 unique amino acid positions wereconfirmed. Improvements of these variants over the parent 2×ObMS rangefrom 12% to 78% based on the competition assay (see Table 9).

TABLE 9 Additional beneficial mutations that were identified fromscreening a second saturation mutagenesis library of 5xObMS. Competitionratios were normalized to that of 5xObMS. The CVs were calculated from 6replicates. Improvement over Residue Synthase variant parent CV 27 H27I12% 1% H27C 17% 3% 28 S28H 55% 5% 207 I207V 50% 4% 222 R222N 53% 3% 342C342L 68% 7% 347 Y347R 37% 5% 382 V382L 23% 1% 390 G390D 60% 3% 401N401I 27% 1% N401V 30% 1% 428 V428L 27% 4% 466 A466C 24% 3% A466S 71% 2%505 C505I 62% 2% C505L 53% 3% C505V 52% 1% 514 G514L 22% 1%

8.10 Generation of Additional Myrcene Synthase Variants—ScreeningCombinatorial Libraries

This example describes methods for combining mutations and screening forimproved myrcene synthase variants using the monoterpene synthasecompetition assay in yeast.

To further improve the activity of myrcene synthase, eight beneficialmutations (K213H, F381L, D389G, I404V, Y439L, R482I, E528D, and M543I)were selected for the design and construction of a combinatoriallibrary. The 5×ObMS was used as the parental sequence. The createdlibrary contained all possible 28 combinations of these eight mutations.To create the combinatorial library, overlapping PCR products and gblocksequences (SEQ ID NOs: 39 to 54) comprising the intended mutations weregenerated. Two PCR reactions were performed with the following primersusing the 5×ObMS as a template:

AMN449: (SEQ ID NO: 29)CTATACTTTAACGTCAAGGAGAAAAAACGGATCCATGGTCGAACCAAGAA GATCCGGTA;  andYY317: (SEQ ID NO: 30) ATAAGCTTCAACCAAATCCAACCAAGACTT.

PCR products were gel purified. A total of sixteen gblocks was used tointroduce all combinations of mutations for F381L, D389G, I404V, Y439L,R482I, E528D, and M543I. Fifty nanograms of each PCR fragment and 10 ngof each gblock were mixed, and an overlap extension PCR reaction wasperformed with Phusion® High-Fidelity DNA Polymerase. The PCR mixturewas first set up without primers, denatured at 95° C. for 3 minutes,followed by 10 cycles (95° C. for 30 seconds, 55° C. for 30 seconds, and72° C. for 2 minutes). The following primers were added to the reaction:

JW730: (SEQ ID NO: 31) TACTTTAACGTCAAGGAGAA ATN009: (SEQ ID NO: 32)TTCAGGTTGTCTAACTCCTTCCTTTTCGG

After addition of primers JW730 and ATN009, the reaction was performedfor another 20 cycles (95° C. for 30 seconds, 56° C. for 30 seconds, and72° C. for 2 minutes). The amplified full length product wasgel-extracted and quantified. 9 ng of the full length product was mixedwith 15 ng of BamHI/NheI digested vector pAM 11614, and gap repairedinto yeast strain Y10566.

To screen the combinatorial library, 800 yeast clones were inoculatedinto wells of 96-well plates, grown and assayed as described previously.Yeast clones with increased myrcene/limonene ratio compared to that ofthe parent strain containing 5×ObMS were identified, and their myrcenesynthase sequences were amplified and sequenced. Over 50 hits with atleast 2-fold improvement over the parent were identified from theinitial Tier-1 screening. A subsequent tier screening led to theconfirmation of the five top hits with improvements (based on thecompetition assay) between 2.5 and 2.8-fold over the parent 5×ObMs (seeTable 10).

TABLE 10 Top five hits identified from screening the myrcene synthasecombinatorial library. Their improvements are relative to the parent ofthe library 5xObMS. Their improvements relative to the enzyme 1xObMS arealso listed for the purpose of tracking the overall progress of myrcenesynthase engineering. Activity Overall relative activity Amino acidmutations to 5xObMS Relative to (as compared to Hit (Parent) 1xObMSwild-type ObMS) T4-2 and 2.5 12.5 F381L, I404V, E528D, M543I T4-36 T4-52.5 12.5 I404V, E528D T4-22 2.5 12.5 F381L, D389G, I404V, Y439L, E528DT4-23 2.5 12.5 F381L, E528D, M5431 T4-43 2.8 14 F381L, I404V, E528D

Sequences of these top hits led to some valuable insights into thesebeneficial mutations. All hits contain the E528D mutation, whichappeared to be one of the best beneficial mutations among the eightmutations included in this combinatorial library. On the other hand,none of the top hits contain either K213H or R482I mutation. Inaddition, there appears to be a synergistic effect between I404V andE528D as the improvement with both mutations together (250% in the HitT4-5 and likely in the Hit T4-43) exceeded the sum of the two individualimprovements (˜110%). In contrast, E528, M543I and F381L mutationsappear to be fully additive when combined, generating a total of 150%improvement in activity as expected from the sum of their individualimprovements (from Table 10). The hit T4-43 which contains three aminoacid changes (F381L, I404V, and E528D) is herein referred to as 14×ObMSvariant because its overall activity is 14 times greater than that of1×ObMS (the wild-type myrcene synthase from Ocimum basilicum).

8.11 Improvement of Myrcene Production in 14×ObMS Variant

This example illustrates improved myrcene production by the ObMSvariants 5×ObMS and 14×ObMS compared to the wild-type 1×ObMS.

Screening host strain X100 was created by integrating two copies ofpGAL1 promoter driven SaGPPS, along with an endonuclease landing pad formyrcene synthases. The landing pad consists of the pGAL1 promoter, theF-CphI cut site, and a terminator. The 1×ObMS, 5×ObMS, and 14×ObMS wereamplified with primers that contain homology to the pGAL1 promoter andthe terminator, and each was cotransformed with pAM2947 plasmidcontaining the F-CphI endonuclease into strains X100 to create newstrains, each with a single copy of 1×ObMS, 5×ObMS, and 14×ObMS,respectively, integrated into the chromosome. These strains were testedfor production in the sealed 2.2 ml 96 well plate model, containing 120μl 1% sucrose, and 30 μl IPM with 1 g/L limonene as an internalstandard. After 72 hours incubation at 30° C. with shaking, the samplesin the plate were analyzed and myrcene production was quantified usingthe headspace analysis as described in Example 7.5.

The results are shown in FIG. 6 . As shown in FIG. 6 , the rapidimprovement has been made to the wild-type 1×ObMS enzyme via combinationof codon optimization (5×ObMS variant) and via a combination of codonoptimization and directed evolution (14×ObMS variant). Compared to thewild-type 1×ObMS nucleic acid (which is not codon optimized), the14×ObMS variant, when expressed in yeast cells, exhibited improvedmyrcene production by about 3.5 fold compared to the wild-type 1×ObMS.

8.12 ObMS Variants with Improvement Over their Parent 14×ObMS

This example describes methods of screening for improved myrcenesynthase variants over their parent 14×ObMS in a monoterpene synthasecompetition assay in yeast.

Site-directed mutagenesis library was created by polymerase chainreaction (PCR) mutagenesis using the 14×ObMS sequence as template. Theparent 14×ObMS enzyme contains three amino acids (F381L, I404V andE528D). Mutations were introduced using degenerate NDT codon on the14×ObMS sequence (SEQ ID NO: 4) as described above in Section 6.9.Primer sequences are listed in Table 7 shown above. Screening andcompetition/headspace assays were carried out as described previously inExamples 6.4, 6.5, and 6.9 using strain Y10566.

Two hits were identified and confirmed from the screening assays. Aftersequencing myrcene synthase sequences in these two hits, the exactchanges in nucleotide sequences were determined. These two hits are:A544S (codon change from get to agt) and Q552R (codon change caa tocgt). The improvements of myrcene synthase activity of these two hitsover the parent 14×ObMS are shown in FIG. 7 , where the Y-axis shows thepercent improvement over the parent enzyme. As shown in FIG. 7 , bothmutations A544S and Q552R improved myrcene synthase activity by at least10% over the parent 14×ObMS.

One or more features from any embodiments described herein or in thefigures may be combined with one or more features of any otherembodiment described herein in the figures without departing from thescope of the invention.

All publications, patents and patent applications cited in thisspecification are herein incorporated by reference as if each individualpublication or patent application were specifically and individuallyindicated to be incorporated by reference. Although the foregoingembodiments have been described in some detail by way of illustrationand example for purposes of clarity of understanding, it will be readilyapparent to those of ordinary skill in the art in light of the teachingsof embodiments of this invention that certain changes and modificationsmay be made thereto without departing from the spirit or scope of theappended claims.

What is claimed:
 1. A genetically modified microbial host cellcomprising: (a) a heterologous nucleic acid molecule encoding an Ocimumspecies myrcene synthase that comprises: an amino acid sequence that hasat least 70% sequence identity to SEQ ID NO: 2, and at least one variantamino acid residue at position 27, 28, 207, 213, 222, 342, 347, 381,382, 389, 390, 401, 404, 428, 439, 466, 482, 484, 505, 514, 517, 524,527, 528, 543, 544, and 552, wherein the positions are numbered withreference to SEQ ID NO: 2; and (b) a heterologous nucleic acid moleculeencoding a geranyl pyrophosphate synthase.
 2. The genetically modifiedmicrobial host cell of claim 1, wherein the heterologous nucleic acidencodes a geranyl pyrophosphate synthase derived from a bacterium. 3.The genetically modified host cell of claim 2, wherein the geranylpyrophosphate synthase is derived from a Streptomyces aculeolatusgeranyl pyrophosphate synthase.
 4. The genetically modified host cell ofclaim 3, wherein the Streptomyces aculeolatus geranyl pyrophosphatesynthase comprises an amino acid sequence having sequence identity toSEQ ID NO:
 7. 5. The genetically modified host cell of claim 1, whereinthe at least one variant amino acid residue is selected from the groupconsisting of H27I, H27C, S28H, 1207 V, K213C, K213H, K213R, K213V,R222N, C342L, Y347R, F381L, V382L, D389G, D389S, G390D, N401I, N401V,I404V, V428L, Y439L, A466C, A466S, R482C, R482D, R482H, R482I, R482L,R482N, R482V, H484Y, C505I, C505L, C505V, G514L, G514V, S517G, F524L,F524V, V527C, V527F, V527H, V527L, V527N, V527S, V527Y, E528D, M543I,A544S, and Q552R, wherein the positions are numbered with reference toSEQ ID NO:
 2. 6. The genetically modified host cell of claim 5, whereinthe myrcene synthase comprises at least one set of variant amino acidresidues compared to SEQ ID NO: 2, and wherein the at least one set ofvariant amino acid residues is selected from the group of sets ofvariant amino acids consisting of: (a) F381L, I404V, E528D, and M543I;(b) I404V and E528D; (c) F381L, D389G, I404V, Y439L, and E528D; (d)F381L, E528D, and M543I; (e) F381L, I404V, and E528D; (f) F381L, I404V,E528D, and A544S; and (g) F381L, I404V, E528D, and Q552R, wherein thepositions are numbered with reference to SEQ ID NO:
 2. 7. Thegenetically modified host cell of claim 6, wherein the myrcene synthasevariant comprises variant amino acid residues F381L, I404V, and E528Dcompared to SEQ ID NO: 2, wherein the positions are numbered withreference to SEQ ID NO:
 2. 8. The genetically modified host cell ofclaim 6, wherein the myrcene synthase variant comprises variant aminoacid residues F381L, I404V, E528D, and A544S compared to SEQ ID NO: 2,wherein the positions are numbered with reference to SEQ ID NO:
 2. 9.The genetically modified host cell of claim 6, wherein the myrcenesynthase variant comprises variant amino acid residues F381L, I404V,E528D, and Q552R compared to SEQ ID NO: 2, wherein the positions arenumbered with reference to SEQ ID NO:
 2. 10. The genetically modifiedhost cell of claim 1, wherein the heterologous nucleic acid moleculeencoding the myrcene synthase comprises a nucleotide sequence having atleast about 70% sequence identity to SEQ ID NO: 1, SEQ ID NO: 3, or SEQID NO:
 4. 11. The genetically modified host cell of claim 10, whereinthe heterologous nucleic acid molecule encoding the myrcene synthasecomprises a nucleotide sequence of SEQ ID NO:
 4. 12. The geneticallymodified host cell of claim 1, wherein the genetically modified hostcell further comprises at least one heterologous mevalonate pathway geneencoding an enzyme selected from the group consisting of: (a) an enzymethat condenses two molecules of acetyl-coenzyme A to formacetoacetyl-CoA; (b) an enzyme that condenses acetoacetyl-CoA withanother molecule of acetyl-CoA to form 3-hydroxy-3-methylglutaryl-CoA(HMG-COA); (c) an enzyme that converts HMG-COA into mevalonate; (d) anenzyme that converts mevalonate into mevalonate 5-phosphate; (e) anenzyme that converts mevalonate 5-phosphate into mevalonate5-pyrophosphate; (f) an enzyme that converts mevalonate 5-pyrophosphateinto IPP; and (g) an enzyme that converts IPP into DMAPP.
 13. Thegenetically modified host cell of claim 1, wherein the geneticallymodified host comprises an endogenous farnesyl pyrophosphate synthasewhich is functionally disrupted to direct carbon flow towards productionof geranyl pyrophosphate.
 14. An isolated nucleic acid molecule encodinga myrcene synthase, wherein the myrcene synthase comprises: (a) an aminoacid sequence that has at least about 70% sequence identity to SEQ IDNO: 2; and (b) at least one variant amino acid residue compared to SEQID NO: 2 at one or more of positions selected from the group ofpositions consisting of positions 27, 28, 207, 213, 222, 342, 347, 381,382, 389, 390, 401, 404, 428, 439, 466, 482, 484, 505, 514, 517, 524,527, 528, 543, 544, and 552, wherein the positions are numbered withreference to SEQ ID NO:
 2. 15. The isolated nucleic acid molecule ofclaim 14, wherein the at least one variant amino acid residue isselected from the group consisting of H27I, H27C, S28H, I207 V, K213C,K213H, K213R, K213V, R222N, C342L, Y347R, F381L, V382L, D389G, D389S,G390D, N401I, N401V, I404V, V428L, Y439L, A466C, A466S, R482C, R482D,R482H, R482I, R482L, R482N, R482V, H484Y, C505I, C505L, C505V, G514L,G514V, S517G, F524L, F524V, V527C, V527F, V527H, V527L, V527N, V527S,V527Y, E528D, M543I, A544S, and Q552R, wherein the positions arenumbered with reference to SEQ ID NO:
 2. 16. The isolated nucleic acidmolecule of claim 15, wherein the myrcene synthase comprises at leastone set of variant amino acid residues compared to SEQ ID NO: 2, andwherein the at least one set of variant amino acid residues is selectedfrom the group of sets of variant amino acid residues consisting of: (a)F381L, I404V, E528D, and M543I; (b) I404V and E528D; (c) F381L, D389G,I404V, Y439L, and E528D; (d) F381L, E528D, and M543I; (e) F381L, I404V,and E528D; (f) F381L, I404V, E528D, and A544S; and (g) F381L, I404V,E528D, and Q552R, wherein the positions are numbered with reference toSEQ ID NO:
 2. 17. The isolated nucleic acid molecule of claim 16,wherein the myrcene synthase variant comprises variant amino acidresidues F381L, I404V, and E528D compared to SEQ ID NO: 2, wherein thepositions are numbered with reference to SEQ ID NO:
 2. 18. The isolatednucleic acid molecule of claim 16, wherein the myrcene synthase variantcomprises variant amino acid residues F381L, I404V, E528D, and A544Scompared to SEQ ID NO: 2, wherein the positions are numbered withreference to SEQ ID NO:
 2. 19. The isolated nucleic acid molecule ofclaim 16, wherein the myrcene synthase variant comprises variant aminoacid residues F381L, I404V, E528D, and Q552R compared to SEQ ID NO: 2,wherein the positions are numbered with reference to SEQ ID NO:
 2. 20.The isolated nucleic acid molecule of claim 14, wherein the isolatednucleic acid molecule comprises a nucleotide sequence having at leastabout 70% sequence identity to SEQ ID NO: 1, SEQ ID NO: 3, or SEQ ID NO:4.
 21. The isolated nucleic acid molecule of claim 20, wherein theisolated nucleic acid molecule comprises a nucleotide sequence of SEQ IDNO:
 4. 22. The isolated nucleic acid molecule of claim 20, wherein theisolated nucleic acid molecule comprises a variant nucleotide sequenceof SEQ ID NO: 3, wherein one or more codons of SEQ ID NO: 3 aresubstituted to encode at least one variant amino acid residue selectedfrom the group consisting of H27I, H27C, S28H, 1207 V, K213C, K213H,K213R, K213V, R222N, C342L, Y347R, F381L, V382L, D389G, D389S, G390D,N401I, N401V, I404V, V428L, Y439L, A466C, A466S, R482C, R482D, R482H,R482I, R482L, R482N, R482V, H484Y, C505I, C505L, C505V, G514L, G514V,S517G, F524L, F524V, V527C, V527F, V527H, V527L, V527N, V527S, V527Y,E528D, M543I, A544S, and Q552R, wherein the positions are numbered withreference to SEQ ID NO:
 2. 23. The isolated nucleic acid molecule ofclaim 20, wherein the isolated nucleic acid molecule comprises a variantnucleotide sequence of SEQ ID NO: 4, wherein one or more codons of SEQID NO: 4 are substituted to encode at least one variant amino acidresidue selected from the group consisting of H27I, H27C, S28H, 1207 V,K213C, K213H, K213R, K213V, R222N, C342L, Y347R, F381L, V382L, D389G,D389S, G390D, N401I, N401V, I404V, V428L, Y439L, A466C, A466S, R482C,R482D, R482H, R482I, R482L, R482N, R482V, H484Y, C505I, C505L, C505V,G514L, G514V, S517G, F524L, F524V, V527C, V527F, V527H, V527L, V527N,V527S, V527Y, E528D, M543I, A544S, and Q552R, wherein the positions arenumbered with reference to SEQ ID NO:
 2. 24. A vector comprising theisolated nucleic acid molecule of claim
 14. 25. A host cell comprisingthe isolated nucleic acid nucleic acid molecule of claim
 14. 26. Amethod of producing myrcene, the method comprising culturing thegenetically modified host cell of claim 1 in a culture medium underculture conditions suitable for production of myrcene.